Commit Graph

183 Commits

Author SHA1 Message Date
Gregory Haskins 45c01e8249 sched: prioritize non-migratable tasks over migratable ones
Dmitry Adamushko pointed out a known flaw in the rt-balancing algorithm
that could allow suboptimal balancing if a non-migratable task gets
queued behind a running migratable one.  It is discussed in this thread:

http://lkml.org/lkml/2008/4/22/296

This issue has been further exacerbated by a recent checkin to
sched-devel (git-id 5eee63a5ebc19a870ac40055c0be49457f3a89a3).

>From a pure priority standpoint, the run-queue is doing the "right"
thing. Using Dmitry's nomenclature, if T0 is on cpu1 first, and T1
wakes up at equal or lower priority (affined only to cpu1) later, it
*should* wait for T0 to finish.  However, in reality that is likely
suboptimal from a system perspective if there are other cores that
could allow T0 and T1 to run concurrently.  Since T1 can not migrate,
the only choice for higher concurrency is to try to move T0.  This is
not something we addessed in the recent rt-balancing re-work.

This patch tries to enhance the balancing algorithm by accomodating this
scenario.  It accomplishes this by incorporating the migratability of a
task into its priority calculation.  Within a numerical tsk->prio, a
non-migratable task is logically higher than a migratable one.  We
maintain this by introducing a new per-priority queue (xqueue, or
exclusive-queue) for holding non-migratable tasks.  The scheduler will
draw from the xqueue over the standard shared-queue (squeue) when
available.

There are several details for utilizing this properly.

1) During task-wake-up, we not only need to check if the priority
   preempts the current task, but we also need to check for this
   non-migratable condition.  Therefore, if a non-migratable task wakes
   up and sees an equal priority migratable task already running, it
   will attempt to preempt it *if* there is a likelyhood that the
   current task will find an immediate home.

2) Tasks only get this non-migratable "priority boost" on wake-up.  Any
   requeuing will result in the non-migratable task being queued to the
   end of the shared queue.  This is an attempt to prevent the system
   from being completely unfair to migratable tasks during things like
   SCHED_RR timeslicing.

I am sure this patch introduces potentially "odd" behavior if you
concoct a scenario where a bunch of non-migratable threads could starve
migratable ones given the right pattern.  I am not yet convinced that
this is a problem since we are talking about tasks of equal RT priority
anyway, and there never is much in the way of guarantees against
starvation under that scenario anyway. (e.g. you could come up with a
similar scenario with a specific timing environment verses an affinity
environment).  I can be convinced otherwise, but for now I think this is
"ok".

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-06-06 15:19:25 +02:00
Ingo Molnar 6363ca57c7 revert ("sched: fair-group: SMP-nice for group scheduling")
Yanmin Zhang reported:

Comparing with 2.6.25, volanoMark has big regression with kernel 2.6.26-rc1.
It's about 50% on my 8-core stoakley, 16-core tigerton, and Itanium Montecito.

With bisect, I located the following patch:

| 18d95a2832 is first bad commit
| commit 18d95a2832
| Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
| Date:   Sat Apr 19 19:45:00 2008 +0200
|
|     sched: fair-group: SMP-nice for group scheduling

Revert it so that we get v2.6.25 behavior.

Bisected-by: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-29 11:28:57 +02:00
Mike Travis 363ab6f142 core: use performance variant for_each_cpu_mask_nr
Change references from for_each_cpu_mask to for_each_cpu_mask_nr
where appropriate

Reviewed-by: Paul Jackson <pj@sgi.com>
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-23 18:35:12 +02:00
Gregory Haskins 8ae121ac86 sched: fix RT task-wakeup logic
Dmitry Adamushko pointed out a logic error in task_wake_up_rt() where we
will always evaluate to "true".  You can find the thread here:

http://lkml.org/lkml/2008/4/22/296

In reality, we only want to try to push tasks away when a wake up request is
not going to preempt the current task.  So lets fix it.

Note: We introduce test_tsk_need_resched() instead of open-coding the flag
check so that the merge-conflict with -rt should help remind us that we
may need to support NEEDS_RESCHED_DELAYED in the future, too.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-05 23:56:18 +02:00
Harvey Harrison 2abdad0a4c sched: make rt_sched_class, idle_sched_class static
The C files are included directly in sched.c, so they are
effectively static.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-05 23:56:17 +02:00
Peter Zijlstra 58d6c2d72f sched: rt-group: optimize dequeue_rt_stack
Now that the group hierarchy can have an arbitrary depth the O(n^2) nature
of RT task dequeues will really hurt. Optimize this by providing space to
store the tree path, so we can walk it the other way.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:45:00 +02:00
Peter Zijlstra 18d95a2832 sched: fair-group: SMP-nice for group scheduling
Implement SMP nice support for the full group hierarchy.

On each load-balance action, compile a sched_domain wide view of the full
task_group tree. We compute the domain wide view when walking down the
hierarchy, and readjust the weights when walking back up.

After collecting and readjusting the domain wide view, we try to balance the
tasks within the task_groups. The current approach is a naively balance each
task group until we've moved the targeted amount of load.

Inspired by Srivatsa Vaddsgiri's previous code and Abhishek Chandra's H-SMP
paper.

XXX: there will be some numerical issues due to the limited nature of
     SCHED_LOAD_SCALE wrt to representing a task_groups influence on the
     total weight. When the tree is deep enough, or the task weight small
     enough, we'll run out of bits.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Abhishek Chandra <chandra@cs.umn.edu>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:45:00 +02:00
Dhaval Giani 354d60c2ff sched: mix tasks and groups
This patch allows tasks and groups to exist in the same cfs_rq. With this
change the CFS group scheduling follows a 1/(M+N) model from a 1/(1+N)
fairness model where M tasks and N groups exist at the cfs_rq level.

[a.p.zijlstra@chello.nl: rt bits and assorted fixes]
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:44:59 +02:00
Mike Travis cd8ba7cd9b sched: add new set_cpus_allowed_ptr function
Add a new function that accepts a pointer to the "newly allowed cpus"
cpumask argument.

int set_cpus_allowed_ptr(struct task_struct *p, const cpumask_t *new_mask)

The current set_cpus_allowed() function is modified to use the above
but this does not result in an ABI change.  And with some compiler
optimization help, it may not introduce any additional overhead.

Additionally, to enforce the read only nature of the new_mask arg, the
"const" property is migrated to sub-functions called by set_cpus_allowed.
This silences compiler warnings.

Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:44:59 +02:00
Peter Zijlstra ac086bc229 sched: rt-group: smp balancing
Currently the rt group scheduling does a per cpu runtime limit, however
the rt load balancer makes no guarantees about an equal spread of real-
time tasks, just that at any one time, the highest priority tasks run.

Solve this by making the runtime limit a global property by borrowing
excessive runtime from the other cpus once the local limit runs out.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:44:58 +02:00
Peter Zijlstra d0b27fa778 sched: rt-group: synchonised bandwidth period
Various SMP balancing algorithms require that the bandwidth period
run in sync.

Possible improvements are moving the rt_bandwidth thing into root_domain
and keeping a span per rt_bandwidth which marks throttled cpus.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:44:57 +02:00
Steven Rostedt 6fa46fa526 sched: balance RT task resched only on runqueue
Sripathi Kodi reported a crash in the -rt kernel:

  https://bugzilla.redhat.com/show_bug.cgi?id=435674

this is due to a place that can reschedule a task without holding
the tasks runqueue lock.  This was caused by the RT balancing code
that pulls RT tasks to the current run queue and will reschedule the
current task.

There's a slight chance that the pulling of the RT tasks will release
the current runqueue's lock and retake it (in the double_lock_balance).
During this time that the runqueue is released, the current task can
migrate to another runqueue.

In the prio_changed_rt code, after the pull, if the current task is of
lesser priority than one of the RT tasks pulled, resched_task is called
on the current task. If the current task had migrated in that small
window, resched_task will be called without holding the runqueue lock
for the runqueue that the task is on.

This race condition also exists in the mainline kernel and this patch
adds a check to make sure the task hasn't migrated before calling
resched_task.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Tested-by: Sripathi Kodi <sripathik@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-07 16:43:00 +01:00
Peter Zijlstra 62fb185130 sched: revert load_balance_monitor() changes
The following commits cause a number of regressions:

  commit 58e2d4ca58
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduling, change how cpu load is calculated

  commit 6b2d770026
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups

Namely:
 - very frequent wakeups on SMP, reported by PowerTop users.
 - cacheline trashing on (large) SMP
 - some latencies larger than 500ms

While there is a mergeable patch to fix the latter, the former issues
are not fixable in a manner suitable for .25 (we're at -rc3 now).

Hence we revert them and try again in v2.6.26.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-04 17:54:06 +01:00
Peter Zijlstra 052f1dc7eb sched: rt-group: make rt groups scheduling configurable
Make the rt group scheduler compile time configurable.
Keep it experimental for now.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-13 15:45:40 +01:00
Peter Zijlstra 9f0c1e560c sched: rt-group: interface
Change the rt_ratio interface to rt_runtime_us, to match rt_period_us.
This avoids picking a granularity for the ratio.

Extend the /sys/kernel/uids/<uid>/ interface to allow setting
the group's rt_runtime.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-13 15:45:39 +01:00
Peter Zijlstra 23b0fdfc92 sched: rt-group: deal with PI
Steven mentioned the fun case where a lock holding task will be throttled.

Simple fix: allow groups that have boosted tasks to run anyway.

If a runnable task in a throttled group gets boosted the dequeue/enqueue
done by rt_mutex_setprio() is enough to unthrottle the group.

This is ofcourse not quite correct. Two possible ways forward are:
  - second prio array for boosted tasks
  - boost to a prio ceiling (this would also work for deadline scheduling)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-13 15:45:39 +01:00
Dmitry Adamushko 326587b840 sched: fix goto retry in pick_next_task_rt()
looking at it one more time:

(1) it looks to me that there is no need to call
sched_rt_ratio_exceeded() from pick_next_rt_entity()

- [ for CONFIG_FAIR_GROUP_SCHED ] queues with rt_rq->rt_throttled are
not within this 'tree-like hierarchy' (or whatever we should call it
:-)

- there is also no need to re-check 'rt_rq->rt_time > ratio' at this
point as 'rt_rq->rt_time' couldn't have been increased since the last
call to update_curr_rt() (which obviously calls
sched_rt_ratio_esceeded())
well, it might be that 'ratio' for this rt_rq has been re-configured
(and the period over which this rt_rq was active has not yet been
finished)... but I don't think we should really take this into
account.

(2) now pick_next_rt_entity() must never return NULL, so let's change
pick_next_task_rt() accordingly.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:34 +01:00
Peter Zijlstra 5a52dd5009 sched: rt-watchdog: fix .rlim_max = RLIM_INFINITY
Remove the curious logic to set it_sched_expires in the future. It useless
because rt.timeout wouldn't be incremented anyway.

Explicity check for RLIM_INFINITY as a test programm that had a 1s soft limit
and a inf hard limit would SIGKILL at 1s. This is because RLIM_INFINITY+d-1
is d-2.

Signed-off-by: Peter Zijlsta <a.p.zijlstra@chello.nl>
CC: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:32 +01:00
Peter Zijlstra 1020387f5f sched: rt-group: reduce rescheduling
Only reschedule if the new group has a higher prio task.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:32 +01:00
Peter Zijlstra 48d5e25821 sched: rt throttling vs no_hz
We need to teach no_hz about the rt throttling because its tick driven.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:31 +01:00
Mike Galbraith 614ee1f61f sched: pull_rt_task() cleanup
"goto out" is an odd way to spell "skip".

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:30 +01:00
Peter Zijlstra 6f505b1642 sched: rt group scheduling
Extend group scheduling to also cover the realtime classes. It uses the time
limiting introduced by the previous patch to allow multiple realtime groups.

The hard time limit is required to keep behaviour deterministic.

The algorithms used make the realtime scheduler O(tg), linear scaling wrt the
number of task groups. This is the worst case behaviour I can't seem to get out
of, the avg. case of the algorithms can be improved, I focused on correctness
and worst case.

[ akpm@linux-foundation.org: move side-effects out of BUG_ON(). ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:30 +01:00
Peter Zijlstra fa85ae2418 sched: rt time limit
Very simple time limit on the realtime scheduling classes.
Allow the rq's realtime class to consume sched_rt_ratio of every
sched_rt_period slice. If the class exceeds this quota the fair class
will preempt the realtime class.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:29 +01:00
Peter Zijlstra 8f4d37ec07 sched: high-res preemption tick
Use HR-timers (when available) to deliver an accurate preemption tick.

The regular scheduler tick that runs at 1/HZ can be too coarse when nice
level are used. The fairness system will still keep the cpu utilisation 'fair'
by then delaying the task that got an excessive amount of CPU time but try to
minimize this by delivering preemption points spot-on.

The average frequency of this extra interrupt is sched_latency / nr_latency.
Which need not be higher than 1/HZ, its just that the distribution within the
sched_latency period is important.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:29 +01:00
Peter Zijlstra 78f2c7db60 sched: SCHED_FIFO/SCHED_RR watchdog timer
Introduce a new rlimit that allows the user to set a runtime timeout on
real-time tasks their slice. Once this limit is exceeded the task will receive
SIGXCPU.

So it measures runtime since the last sleep.

Input and ideas by Thomas Gleixner and Lennart Poettering.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Lennart Poettering <mzxreary@0pointer.de>
CC: Michael Kerrisk <mtk.manpages@googlemail.com>
CC: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:27 +01:00
Peter Zijlstra fa717060f1 sched: sched_rt_entity
Move the task_struct members specific to rt scheduling together.
A future optimization could be to put sched_entity and sched_rt_entity
into a union.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:27 +01:00
Gregory Haskins c49443c538 sched: remove some old cpuset logic
We had support for overlapping cpuset based rto logic in early
prototypes that is no longer used, so remove it.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:23 +01:00
Gregory Haskins cdc8eb984c sched: RT-balance, only adjust overload state when changing
The overload set/clears were originally idempotent when this logic was first
implemented.  But that is no longer true due to the addition of the atomic
counter and this logic was never updated to work properly with that change.
So only adjust the overload state if it is actually changing to avoid
getting out of sync.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:23 +01:00
Steven Rostedt cb46984504 sched: RT-balance, add new methods to sched_class
Dmitry Adamushko found that the current implementation of the RT
balancing code left out changes to the sched_setscheduler and
rt_mutex_setprio.

This patch addresses this issue by adding methods to the schedule classes
to handle being switched out of (switched_from) and being switched into
(switched_to) a sched_class. Also a method for changing of priorities
is also added (prio_changed).

This patch also removes some duplicate logic between rt_mutex_setprio and
sched_setscheduler.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:22 +01:00
Steven Rostedt 9a897c5a67 sched: RT-balance, replace hooks with pre/post schedule and wakeup methods
To make the main sched.c code more agnostic to the schedule classes.
Instead of having specific hooks in the schedule code for the RT class
balancing. They are replaced with a pre_schedule, post_schedule
and task_wake_up methods. These methods may be used by any of the classes
but currently, only the sched_rt class implements them.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:22 +01:00
Ingo Molnar bdd7c81b49 sched: fix sched_rt.c:join/leave_domain
fix build bug in sched_rt.c:join/leave_domain and make them only
be included on SMP builds.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:18 +01:00
Gregory Haskins 637f50851b sched: only balance our RT tasks within our domain
We move the rt-overload data as the first global to per-domain
reclassification.  This limits the scope of overload related cache-line
bouncing to stay with a specified partition instead of affecting all
cpus in the system.

Finally, we limit the scope of find_lowest_cpu searches to the domain
instead of the entire system.  Note that we would always respect domain
boundaries even without this patch, but we first would scan potentially
all cpus before whittling the list down.  Now we can avoid looking at
RQs that are out of scope, again reducing cache-line hits.

Note: In some cases, task->cpus_allowed will effectively reduce our search
to within our domain.  However, I believe there are cases where the
cpus_allowed mask may be all ones and therefore we err on the side of
caution.  If it can be optimized later, so be it.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:18 +01:00
Ingo Molnar 7f51f29820 sched: clean up schedule_balance_rt()
clean up schedule_balance_rt().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:17 +01:00
Ingo Molnar 80bf3171dc sched: clean up pull_rt_task()
clean up pull_rt_task().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:17 +01:00
Ingo Molnar 00597c3ed7 sched: remove leftover debugging
remove leftover debugging.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:16 +01:00
Ingo Molnar 6e1938d3ad sched: remove rt_overload()
remove rt_overload() - it's an unnecessary indirection.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:16 +01:00
Ingo Molnar 84de427489 sched: clean up kernel/sched_rt.c
clean up whitespace damage and missing comments in kernel/sched_rt.c.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:15 +01:00
Ingo Molnar deeeccd41b sched: clean up overlong line in kernel/sched_debug.c
clean up overlong line in kernel/sched_debug.c.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:15 +01:00
Ingo Molnar 4df64c0bfb sched: clean up find_lock_lowest_rq()
clean up find_lock_lowest_rq().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:15 +01:00
Ingo Molnar 79064fbf75 sched: clean up pick_next_highest_task_rt()
clean up pick_next_highest_task_rt().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:14 +01:00
Steven Rostedt 610bf05645 sched: RT-balance, optimize cpu search
This patch removes several cpumask operations by keeping track
of the first of the CPUS that is of the lowest priority. When
the search for the lowest priority runqueue is completed, all
the bits up to the first CPU with the lowest priority runqueue
is cleared.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:13 +01:00
Gregory Haskins 06f90dbd76 sched: RT-balance, optimize
We can cheaply track the number of bits set in the cpumask for the lowest
priority CPUs.  Therefore, compute the mask's weight and use it to skip
the optimal domain search logic when there is only one CPU available.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:13 +01:00
Gregory Haskins 17b3279b48 sched: break out early if RT task cannot be migrated
We don't need to bother searching if the task cannot be migrated

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:13 +01:00
Steven Rostedt e1f47d891c sched: RT-balance, avoid overloading
This patch changes the searching for a run queue by a waking RT task
to try to pick another runqueue if the currently running task
is an RT task.

The reason is that RT tasks behave different than normal
tasks. Preempting a normal task to run a RT task to keep
its cache hot is fine, because the preempted non-RT task
may wait on that same runqueue to run again unless the
migration thread comes along and pulls it off.

RT tasks behave differently. If one is preempted, it makes
an active effort to continue to run. So by having a high
priority task preempt a lower priority RT task, that lower
RT task will then quickly try to run on another runqueue.
This will cause that lower RT task to replace its nice
hot cache (and TLB) with a completely cold one. This is
for the hope that the new high priority RT task will keep
 its cache hot.

Remeber that this high priority RT task was just woken up.
So it may likely have been sleeping for several milliseconds,
and will end up with a cold cache anyway. RT tasks run till
they voluntarily stop, or are preempted by a higher priority
task. This means that it is unlikely that the woken RT task
will have a hot cache to wake up to. So pushing off a lower
RT task is just killing its cache for no good reason.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:12 +01:00
Gregory Haskins a22d7fc187 sched: wake-balance fixes
We have logic to detect whether the system has migratable tasks, but we are
not using it when deciding whether to push tasks away.  So we add support
for considering this new information.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:12 +01:00
Gregory Haskins 6e1254d2c4 sched: optimize RT affinity
The current code base assumes a relatively flat CPU/core topology and will
route RT tasks to any CPU fairly equally.  In the real world, there are
various toplogies and affinities that govern where a task is best suited to
run with the smallest amount of overhead.  NUMA and multi-core CPUs are
prime examples of topologies that can impact cache performance.

Fortunately, linux is already structured to represent these topologies via
the sched_domains interface.  So we change our RT router to consult a
combination of topology and affinity policy to best place tasks during
migration.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:11 +01:00
Gregory Haskins 318e0893ce sched: pre-route RT tasks on wakeup
In the original patch series that Steven Rostedt and I worked on together,
we both took different approaches to low-priority wakeup path.  I utilized
"pre-routing" (push the task away to a less important RQ before activating)
approach, while Steve utilized a "post-routing" approach.  The advantage of
my approach is that you avoid the overhead of a wasted activate/deactivate
cycle and peripherally related burdens.  The advantage of Steve's method is
that it neatly solves an issue preventing a "pull" optimization from being
deployed.

In the end, we ended up deploying Steve's idea.  But it later dawned on me
that we could get the best of both worlds by deploying both ideas together,
albeit slightly modified.

The idea is simple:  Use a "light-weight" lookup for pre-routing, since we
only need to approximate a good home for the task.  And we also retain the
post-routing push logic to clean up any inaccuracies caused by a condition
of "priority mistargeting" caused by the lightweight lookup.  Most of the
time, the pre-routing should work and yield lower overhead.  In the cases
where it doesnt, the post-router will bat cleanup.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:10 +01:00
Gregory Haskins 2de0b4639f sched: RT balancing: include current CPU
It doesn't hurt if we allow the current CPU to be included in the
search.  We will just simply skip it later if the current CPU turns out
to be the lowest.

We will use this later in the series

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:10 +01:00
Gregory Haskins 07b4032c9e sched: break out search for RT tasks
Isolate the search logic into a function so that it can be used later
in places other than find_locked_lowest_rq().

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:10 +01:00
Gregory Haskins e7693a362e sched: de-SCHED_OTHER-ize the RT path
The current wake-up code path tries to determine if it can optimize the
wake-up to "this_cpu" by computing load calculations.  The problem is that
these calculations are only relevant to SCHED_OTHER tasks where load is king.
For RT tasks, priority is king.  So the load calculation is completely wasted
bandwidth.

Therefore, we create a new sched_class interface to help with
pre-wakeup routing decisions and move the load calculation as a function
of CFS task's class.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:09 +01:00
Gregory Haskins 697f0a487f sched: clean up this_rq use in kernel/sched_rt.c
"this_rq" is normally used to denote the RQ on the current cpu
(i.e. "cpu_rq(this_cpu)").  So clean up the usage of this_rq to be
more consistent with the rest of the code.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:09 +01:00
Gregory Haskins 73fe6aae84 sched: add RT-balance cpu-weight
Some RT tasks (particularly kthreads) are bound to one specific CPU.
It is fairly common for two or more bound tasks to get queued up at the
same time.  Consider, for instance, softirq_timer and softirq_sched.  A
timer goes off in an ISR which schedules softirq_thread to run at RT50.
Then the timer handler determines that it's time to smp-rebalance the
system so it schedules softirq_sched to run.  So we are in a situation
where we have two RT50 tasks queued, and the system will go into
rt-overload condition to request other CPUs for help.

This causes two problems in the current code:

1) If a high-priority bound task and a low-priority unbounded task queue
   up behind the running task, we will fail to ever relocate the unbounded
   task because we terminate the search on the first unmovable task.

2) We spend precious futile cycles in the fast-path trying to pull
   overloaded tasks over.  It is therefore optimial to strive to avoid the
   overhead all together if we can cheaply detect the condition before
   overload even occurs.

This patch tries to achieve this optimization by utilizing the hamming
weight of the task->cpus_allowed mask.  A weight of 1 indicates that
the task cannot be migrated.  We will then utilize this information to
skip non-migratable tasks and to eliminate uncessary rebalance attempts.

We introduce a per-rq variable to count the number of migratable tasks
that are currently running.  We only go into overload if we have more
than one rt task, AND at least one of them is migratable.

In addition, we introduce a per-task variable to cache the cpus_allowed
weight, since the hamming calculation is probably relatively expensive.
We only update the cached value when the mask is updated which should be
relatively infrequent, especially compared to scheduling frequency
in the fast path.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:07 +01:00
Steven Rostedt c7a1e46aa9 sched: disable standard balancer for RT tasks
Since we now take an active approach to load balancing, we don't need to
balance RT tasks via the normal task balancer. In fact, this code was
found to pull RT tasks away from CPUS that the active movement performed,
resulting in large latencies.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:07 +01:00
Steven Rostedt 4642dafdf9 sched: push RT tasks from overloaded CPUs
This patch adds pushing of overloaded RT tasks from a runqueue that is
having tasks (most likely RT tasks) added to the run queue.

TODO: We don't cover the case of waking of new RT tasks (yet).

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:07 +01:00
Steven Rostedt f65eda4f78 sched: pull RT tasks from overloaded runqueues
This patch adds the algorithm to pull tasks from RT overloaded runqueues.

When a pull RT is initiated, all overloaded runqueues are examined for
a RT task that is higher in prio than the highest prio task queued on the
target runqueue. If another runqueue holds a RT task that is of higher
prio than the highest prio task on the target runqueue is found it is pulled
to the target runqueue.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:07 +01:00
Steven Rostedt 4fd29176b7 sched: add rt-overload tracking
This patch adds an RT overload accounting system. When a runqueue has
more than one RT task queued, it is marked as overloaded. That is that it
is a candidate to have RT tasks pulled from it.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:06 +01:00
Steven Rostedt e8fa136262 sched: add RT task pushing
This patch adds an algorithm to push extra RT tasks off a run queue to
other CPU runqueues.

When more than one RT task is added to a run queue, this algorithm takes
an assertive approach to push the RT tasks that are not running onto other
run queues that have lower priority.  The way this works is that the highest
RT task that is not running is looked at and we examine the runqueues on
the CPUS for that tasks affinity mask. We find the runqueue with the lowest
prio in the CPU affinity of the picked task, and if it is lower in prio than
the picked task, we push the task onto that CPU runqueue.

We continue pushing RT tasks off the current runqueue until we don't push any
more.  The algorithm stops when the next highest RT task can't preempt any
other processes on other CPUS.

TODO: The algorithm may stop when there are still RT tasks that can be
 migrated. Specifically, if the highest non running RT task CPU affinity
 is restricted to CPUs that are running higher priority tasks, there may
 be a lower priority task queued that has an affinity with a CPU that is
 running a lower priority task that it could be migrated to.  This
 patch set does not address this issue.

Note: checkpatch reveals two over 80 character instances. I'm not sure
 that breaking them up will help visually, so I left them as is.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:05 +01:00
Steven Rostedt 764a9d6fe4 sched: track highest prio task queued
This patch adds accounting to each runqueue to keep track of the
highest prio task queued on the run queue. We only care about
RT tasks, so if the run queue does not contain any active RT tasks
its priority will be considered MAX_RT_PRIO.

This information will be used for later patches.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:04 +01:00
Steven Rostedt 63489e45e2 sched: count # of queued RT tasks
This patch adds accounting to keep track of the number of RT tasks running
on a runqueue. This information will be used in later patches.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:03 +01:00
Srivatsa Vaddagiri 58e2d4ca58 sched: group scheduling, change how cpu load is calculated
This patch changes how the cpu load exerted by fair_sched_class tasks
is calculated. Load exerted by fair_sched_class tasks on a cpu is now
a summation of the group weights, rather than summation of task weights.
Weight exerted by a group on a cpu is dependent on the shares allocated
to it.

This version of patch has a minor impact on code size, but should have
no runtime/functional impact for !CONFIG_FAIR_GROUP_SCHED.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:00 +01:00
Peter Zijlstra 67e2be0232 sched: rt: account the cpu time during the tick
Realtime tasks would not account their runtime during ticks. Which would lead
to:

        struct sched_param param = { .sched_priority = 10 };
        pthread_setschedparam(pthread_self(), SCHED_FIFO, &param);

	while (1) ;

Not showing up in top.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2007-12-20 15:01:17 +01:00
Srivatsa Vaddagiri d842de871c sched: cpu accounting controller (V2)
Commit cfb5285660 removed a useful feature for
us, which provided a cpu accounting resource controller.  This feature would be
useful if someone wants to group tasks only for accounting purpose and doesnt
really want to exercise any control over their cpu consumption.

The patch below reintroduces the feature. It is based on Paul Menage's
original patch (Commit 62d0df6406), with
these differences:

        - Removed load average information. I felt it needs more thought (esp
	  to deal with SMP and virtualized platforms) and can be added for
	  2.6.25 after more discussions.
        - Convert group cpu usage to be nanosecond accurate (as rest of the cfs
	  stats are) and invoke cpuacct_charge() from the respective scheduler
	  classes
	- Make accounting scalable on SMP systems by splitting the usage
	  counter to be per-cpu
	- Move the code from kernel/cpu_acct.c to kernel/sched.c (since the
	  code is not big enough to warrant a new file and also this rightly
	  needs to live inside the scheduler. Also things like accessing
	  rq->lock while reading cpu usage becomes easier if the code lived in
	  kernel/sched.c)

The patch also modifies the cpu controller not to provide the same accounting
information.

Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com>

 Tested the patches on top of 2.6.24-rc3. The patches work fine. Ran
 some simple tests like cpuspin (spin on the cpu), ran several tasks in
 the same group and timed them. Compared their time stamps with
 cpuacct.usage.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-12-02 20:04:49 +01:00
Peter Williams 681f3e6854 sched: isolate SMP balancing code a bit more
At the moment, a lot of load balancing code that is irrelevant to non
SMP systems gets included during non SMP builds.

This patch addresses this issue and reduces the binary size on non
SMP systems:

   text    data     bss     dec     hex filename
  10983      28    1192   12203    2fab sched.o.before
  10739      28    1192   11959    2eb7 sched.o.after

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-24 18:23:51 +02:00
Peter Williams e1d1484f72 sched: reduce balance-tasks overhead
At the moment, balance_tasks() provides low level functionality for both
  move_tasks() and move_one_task() (indirectly) via the load_balance()
function (in the sched_class interface) which also provides dual
functionality.  This dual functionality complicates the interfaces and
internal mechanisms and makes the run time overhead of operations that
are called with two run queue locks held.

This patch addresses this issue and reduces the overhead of these
operations.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-24 18:23:51 +02:00
Dmitry Adamushko a4ec24b48d sched: tidy up SCHED_RR
- make timeslices of SCHED_RR tasks constant and not
dependent on task's static_prio [1] ;
- remove obsolete code (timeslice related bits);
- make sched_rr_get_interval() return something more
meaningful [2] for SCHED_OTHER tasks.

[1] according to the following link, it's not compliant with SUSv3
(not sure though, what is the reference for us :-)
http://lkml.org/lkml/2007/3/7/656

[2] the interval is dynamic and can be depicted as follows "should a
task be one of the runnable tasks at this particular moment, it would
expect to run for this interval of time before being re-scheduled by the
scheduler tick".
(i.e. it's more precise if a task is runnable at the moment)

yeah, this seems to require task_rq_lock/unlock() but this is not a hot
path.

results:

(SCHED_FIFO)

dimm@earth:~/storage/prog$ sudo chrt -f 10 ./rr_interval 
time_slice: 0 : 0

(SCHED_RR)

dimm@earth:~/storage/prog$ sudo chrt 10 ./rr_interval 
time_slice: 0 : 99984800

(SCHED_NORMAL)

dimm@earth:~/storage/prog$ ./rr_interval 
time_slice: 0 : 19996960

(SCHED_NORMAL + a cpu_hog of similar 'weight' on the same CPU --- so should be a half of the previous result)

dimm@earth:~/storage/prog$ taskset 1 ./rr_interval 
time_slice: 0 : 9998480

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:13 +02:00
Alexey Dobriyan a9957449b0 sched: uninline scheduler
* save ~300 bytes
* activate_idle_task() was moved to avoid a warning

bloat-o-meter output:

add/remove: 6/0 grow/shrink: 0/16 up/down: 438/-733 (-295)		<===
function                                     old     new   delta
__enqueue_entity                               -     165    +165
finish_task_switch                             -     110    +110
update_curr_rt                                 -      79     +79
__load_balance_iterator                        -      32     +32
__task_rq_unlock                               -      28     +28
find_process_by_pid                            -      24     +24
do_sched_setscheduler                        133     123     -10
sys_sched_rr_get_interval                    176     165     -11
sys_sched_getparam                           156     145     -11
normalize_rt_tasks                           482     470     -12
sched_getaffinity                            112      99     -13
sys_sched_getscheduler                        86      72     -14
sched_setaffinity                            226     212     -14
sched_setscheduler                           666     642     -24
load_balance_start_fair                       33       9     -24
load_balance_next_fair                        33       9     -24
dequeue_task_rt                              133      67     -66
put_prev_task_rt                              97      28     -69
schedule_tail                                133      50     -83
schedule                                     682     594     -88
enqueue_entity                               499     366    -133
task_new_fair                                317     180    -137

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:13 +02:00
Ingo Molnar 5522d5d5f7 sched: mark scheduling classes as const
mark scheduling classes as const. The speeds up the code
a bit and shrinks it:

   text    data     bss     dec     hex filename
  40027    4018     292   44337    ad31 sched.o.before
  40190    3842     292   44324    ad24 sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
2007-10-15 17:00:12 +02:00
Srivatsa Vaddagiri 83b699ed20 sched: revert recent removal of set_curr_task()
Revert removal of set_curr_task.
Use put_prev_task/set_curr_task when changing groups/policies

Signed-off-by: Srivatsa Vaddagiri < vatsa@linux.vnet.ibm.com>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
2007-10-15 17:00:08 +02:00
Dmitry Adamushko f6b53205e1 sched: rework enqueue/dequeue_entity() to get rid of set_curr_task()
rework enqueue/dequeue_entity() to get rid of 
sched_class::set_curr_task(). This simplifies sched_setscheduler(), 
rt_mutex_setprio() and sched_move_tasks().

   text    data     bss     dec     hex filename
  24330    2734      20   27084    69cc sched.o.before
  24233    2730      20   26983    6967 sched.o.after

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
2007-10-15 17:00:08 +02:00
Dmitry Adamushko 4530d7ab0f sched: simplify sched_class::yield_task()
the 'p' (task_struct) parameter in the sched_class :: yield_task() is
redundant as the caller is always the 'current'. Get rid of it.

   text    data     bss     dec     hex filename
  24341    2734      20   27095    69d7 sched.o.before
  24330    2734      20   27084    69cc sched.o.after

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
2007-10-15 17:00:08 +02:00
Srivatsa Vaddagiri 29f59db3a7 sched: group-scheduler core
Add interface to control cpu bandwidth allocation to task-groups.

(not yet configurable, due to missing CONFIG_CONTAINERS)

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
2007-10-15 17:00:07 +02:00
Dmitry Adamushko 98fbc79853 sched: optimize task_tick_rt() a bit
Mitchell Erblich suggested a quality-of-implementation change to
not requeue SCHED_RR tasks if there's only a single task on the
runqueue, by checking for rq->nr_running == 1.

provide a more efficient implementation of that, to check that
particular RT priority-queue only.

[ From: mingo@elte.hu ]

Also first requeue the task then set need_resched - results in slightly
better machine-instruction ordering. Also clean up the code a bit.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-24 20:39:10 +02:00
Ingo Molnar 31ee529cc2 sched: remove the 'u64 now' parameter from ->put_prev_task()
remove the 'u64 now' parameter from ->put_prev_task().

( identity transformation that causes no change in functionality. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:49 +02:00
Ingo Molnar fb8d472402 sched: remove the 'u64 now' parameter from ->pick_next_task()
remove the 'u64 now' parameter from ->pick_next_task().

( identity transformation that causes no change in functionality. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:48 +02:00
Ingo Molnar f02231e51a sched: remove the 'u64 now' parameter from ->dequeue_task()
remove the 'u64 now' parameter from ->dequeue_task().

( identity transformation that causes no change in functionality. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:48 +02:00
Ingo Molnar fd390f6a04 sched: remove the 'u64 now' parameter from ->enqueue_task()
remove the 'u64 now' parameter from ->enqueue_task().

( identity transformation that causes no change in functionality. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:48 +02:00
Ingo Molnar f1e14ef64d sched: remove the 'u64 now' parameter from update_curr_rt()
remove the 'u64 now' parameter from update_curr_rt().

( identity transformation that causes no change in functionality. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:48 +02:00
Ingo Molnar d281918d7c sched: remove 'now' use from assignments
change all 'now' timestamp uses in assignments to rq->clock.

( this is an identity transformation that causes no functionality change:
  all such new rq->clock is necessarily preceded by an update_rq_clock()
  call. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:47 +02:00
Peter Williams a4ac01c36e sched: fix bug in balance_tasks()
There are two problems with balance_tasks() and how it used:

1. The variables best_prio and best_prio_seen (inherited from the old
move_tasks()) were only required to handle problems caused by the
active/expired arrays, the order in which they were processed and the
possibility that the task with the highest priority could be on either.
  These issues are no longer present and the extra overhead associated
with their use is unnecessary (and possibly wrong).

2. In the absence of CONFIG_FAIR_GROUP_SCHED being set, the same
this_best_prio variable needs to be used by all scheduling classes or
there is a risk of moving too much load.  E.g. if the highest priority
task on this at the beginning is a fairly low priority task and the rt
class migrates a task (during its turn) then that moved task becomes the
new highest priority task on this_rq but when the sched_fair class
initializes its copy of this_best_prio it will get the priority of the
original highest priority task as, due to the run queue locks being
held, the reschedule triggered by pull_task() will not have taken place.
  This could result in inappropriate overriding of skip_for_load and
excessive load being moved.

The attached patch addresses these problems by deleting all reference to
best_prio and best_prio_seen and making this_best_prio a reference
parameter to the various functions involved.

load_balance_fair() has also been modified so that this_best_prio is
only reset (in the loop) if CONFIG_FAIR_GROUP_SCHED is set.  This should
preserve the effect of helping spread groups' higher priority tasks
around the available CPUs while improving system performance when
CONFIG_FAIR_GROUP_SCHED isn't set.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:46 +02:00
Peter Williams 4301065920 sched: simplify move_tasks()
The move_tasks() function is currently multiplexed with two distinct
capabilities:

1. attempt to move a specified amount of weighted load from one run
queue to another; and
2. attempt to move a specified number of tasks from one run queue to
another.

The first of these capabilities is used in two places, load_balance()
and load_balance_idle(), and in both of these cases the return value of
move_tasks() is used purely to decide if tasks/load were moved and no
notice of the actual number of tasks moved is taken.

The second capability is used in exactly one place,
active_load_balance(), to attempt to move exactly one task and, as
before, the return value is only used as an indicator of success or failure.

This multiplexing of sched_task() was introduced, by me, as part of the
smpnice patches and was motivated by the fact that the alternative, one
function to move specified load and one to move a single task, would
have led to two functions of roughly the same complexity as the old
move_tasks() (or the new balance_tasks()).  However, the new modular
design of the new CFS scheduler allows a simpler solution to be adopted
and this patch addresses that solution by:

1. adding a new function, move_one_task(), to be used by
active_load_balance(); and
2. making move_tasks() a single purpose function that tries to move a
specified weighted load and returns 1 for success and 0 for failure.

One of the consequences of these changes is that neither move_one_task()
or the new move_tasks() care how many tasks sched_class.load_balance()
moves and this enables its interface to be simplified by returning the
amount of load moved as its result and removing the load_moved pointer
from the argument list.  This helps simplify the new move_tasks() and
slightly reduces the amount of work done in each of
sched_class.load_balance()'s implementations.

Further simplification, e.g. changes to balance_tasks(), are possible
but (slightly) complicated by the special needs of load_balance_fair()
so I've left them to a later patch (if this one gets accepted).

NB Since move_tasks() gets called with two run queue locks held even
small reductions in overhead are worthwhile.

[ mingo@elte.hu ]

this change also reduces code size nicely:

   text    data     bss     dec     hex filename
   39216    3618      24   42858    a76a sched.o.before
   39173    3618      24   42815    a73f sched.o.after

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09 11:16:46 +02:00
Ingo Molnar 6cfb0d5d06 [PATCH] sched: reduce debug code
move the rest of the debugging/instrumentation code to under
CONFIG_SCHEDSTATS too. This reduces code size and speeds code up:

    text    data     bss     dec     hex filename
   33044    4122      28   37194    914a sched.o.before
   32708    4122      28   36858    8ffa sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-02 17:41:40 +02:00
Ingo Molnar cad60d93e1 [PATCH] sched: ->task_new cleanup
make sched_class.task_new == NULL a 'default method', this
allows the removal of task_rt_new.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-02 17:41:40 +02:00
Ingo Molnar bb44e5d1c6 sched: cfs core, kernel/sched_rt.c
add kernel/sched_rt.c: SCHED_FIFO/SCHED_RR support. The behavior
and semantics of SCHED_FIFO/SCHED_RR tasks is unchanged.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-07-09 18:51:58 +02:00