linux/kernel/sched
Peter Zijlstra 2548d546d4 nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick()
Chris Metcalf reported a that sched_can_stop_tick() sometimes fails to
re-enable the tick.

His observed problem is that rq->cfs.nr_running can be 1 even though
there are multiple runnable CFS tasks. This happens in the cgroup
case, in which case cfs.nr_running is the number of runnable entities
for that level.

If there is a single runnable cgroup (which can have an arbitrary
number of runnable child entries itself) rq->cfs.nr_running will be 1.

However, looking at that function I think there's more problems with it.

It seems to assume that if there's FIFO tasks, those will run. This is
incorrect. The FIFO task can have a lower prio than an RR task, in which
case the RR task will run.

So the whole fifo_nr_running test seems misplaced, it should go after
the rr_nr_running tests. That is, only if !rr_nr_running, can we use
fifo_nr_running like this.

Reported-by: Chris Metcalf <cmetcalf@mellanox.com>
Tested-by: Chris Metcalf <cmetcalf@mellanox.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <kernellwp@gmail.com>
Fixes: 76d92ac305 ("sched: Migrate sched to use new tick dependency mask model")
Link: http://lkml.kernel.org/r/20160421160315.GK24771@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28 10:28:55 +02:00
..
Makefile kernel: add kcov code coverage 2016-03-22 15:36:02 -07:00
auto_group.c sched/core: Move the sched_to_prio[] arrays out of line 2015-12-04 10:34:46 +01:00
auto_group.h sched, timer: Convert usages of ACCESS_ONCE() in the scheduler to READ_ONCE()/WRITE_ONCE() 2015-05-08 12:11:32 +02:00
clock.c sched-clock: Migrate to use new tick dependency mask model 2016-03-02 16:44:57 +01:00
completion.c sched/completion: Serialize completion_done() with complete() 2015-02-18 14:27:40 +01:00
core.c nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick() 2016-04-28 10:28:55 +02:00
cpuacct.c Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-03-24 09:42:50 -07:00
cpuacct.h sched/cpuacct: Simplify the cpuacct code 2016-03-21 11:00:28 +01:00
cpudeadline.c sched/deadline: Unify dl_time_before() usage 2015-09-23 09:51:25 +02:00
cpudeadline.h sched/deadline: Unify dl_time_before() usage 2015-09-23 09:51:25 +02:00
cpufreq.c cpufreq: Move scheduler-related code to the sched directory 2016-03-10 20:44:47 +01:00
cpupri.c Merge commit '3cf2f34' into sched/core, to fix build error 2014-06-12 13:46:37 +02:00
cpupri.h sched/cpupri: Remove unnecessary definitions in cpupri.h 2014-11-16 10:58:59 +01:00
cputime.c sched/cputime: Fix steal_account_process_tick() to always return jiffies 2016-03-08 12:24:56 +01:00
deadline.c Power management and ACPI material for v4.6-rc1, part 1 2016-03-16 14:10:53 -07:00
debug.c sched/debug: Add deadline scheduler bandwidth ratio to /proc/sched_debug 2016-02-29 09:53:07 +01:00
fair.c Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-03-24 09:42:50 -07:00
features.h sched/fair: Convert arch_scale_cpu_capacity() from weak function to #define 2015-09-13 09:52:55 +02:00
idle.c rcu: Make CPU_DYING_IDLE an explicit call 2016-03-01 20:36:58 +01:00
idle_task.c sched/fair: Remove empty idle enter and exit functions 2015-11-23 09:37:51 +01:00
loadavg.c sched: Move the loadavg code to a more obvious location 2015-05-08 12:04:12 +02:00
rt.c Power management and ACPI material for v4.6-rc1, part 1 2016-03-16 14:10:53 -07:00
sched.h Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-03-24 09:42:50 -07:00
stats.c sched: use %*pb[l] to print bitmaps including cpumasks and nodemasks 2015-02-13 21:21:37 -08:00
stats.h sched/debug: Make schedstats a runtime tunable that is disabled by default 2016-02-09 11:54:23 +01:00
stop_task.c sched: Make sched_class::set_cpus_allowed() unconditional 2015-08-12 12:06:09 +02:00
swait.c wait.[ch]: Introduce the simple waitqueue (swait) implementation 2016-02-25 11:27:16 +01:00
wait.c sched/wait: Fix the signal handling fix 2015-12-13 14:30:59 -08:00