Commit Graph

131 Commits

Author SHA1 Message Date
Jens Axboe d6de8be711 cfq-iosched: fix RCU problem in cfq_cic_lookup()
cfq_cic_lookup() needs to properly protect ioc->ioc_data before
dereferencing it and also exclude updaters of ioc->ioc_data as well.

Also add a number of comments documenting why the existing RCU usage
is OK.

Thanks a lot to "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> for
review and comments!

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-28 14:49:28 +02:00
Richard Kennedy be754d2c21 block: reorder cfq_queue to save space on 64bit builds
saves 8 bytes of padding & increases objects/slab from 30 to 32 on my
AMD64 config

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-28 14:49:27 +02:00
Jens Axboe 6d63c27557 cfq-iosched: make io priorities inherit CPU scheduling class as well as nice
We currently set all processes to the best-effort scheduling class,
regardless of what CPU scheduling class they belong to. Improve that
so that we correctly track idle and rt scheduling classes as well.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-07 09:51:23 +02:00
Jens Axboe 07416d29bc cfq-iosched: fix RCU race in the cfq io_context destructor handling
put_io_context() drops the RCU read lock before calling into cfq_dtor(),
however we need to hold off freeing there before grabbing and
dereferencing the first object on the list.

So extend the rcu_read_lock() scope to cover the calling of cfq_dtor(),
and optimize cfq_free_io_context() to use a new variant for
call_for_each_cic() that assumes the RCU read lock is already held.

Hit in the wild by Alexey Dobriyan <adobriyan@gmail.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-07 09:28:57 +02:00
Fabio Checconi 4faa3c8150 cfq-iosched: do not leak ioc_data across iosched switches
When switching scheduler from cfq, cfq_exit_queue() does not clear
ioc->ioc_data, leaving a dangling pointer that can deceive the following
lookups when the iosched is switched back to cfq.  The pattern that can
trigger that is the following:

    - elevator switch from cfq to something else;
    - module unloading, with elv_unregister() that calls cfq_free_io_context()
      on ioc freeing the cic (via the .trim op);
    - module gets reloaded and the elevator switches back to cfq;
    - reallocation of a cic at the same address as before (with a valid key).

To fix it just assign NULL to ioc_data in __cfq_exit_single_io_context(),
that is called from the regular exit path and from the elevator switching
code.  The only path that frees a cic and is not covered is the error handling
one, but cic's freed in this way are never cached in ioc_data.

Signed-off-by: Fabio Checconi <fabio@gandalf.sssup.it>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-04-10 08:28:01 +02:00
Fabio Checconi 34e6bbf23c cfq-iosched: fix rcu freeing of cfq io contexts
SLAB_DESTROY_BY_RCU is not a direct substitute for normal call_rcu()
freeing, since it'll page freeing but NOT object freeing. So change
cfq to do the freeing on its own.

Signed-off-by: Fabio Checconi <fabio@gandalf.sssup.it>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-04-02 15:42:20 +02:00
Jens Axboe ffc4e75957 cfq-iosched: add hlist for browsing parallel to the radix tree
It's cumbersome to browse a radix tree from start to finish, especially
since we modify keys when a process exits. So add a hlist for the single
purpose of browsing over all known cfq_io_contexts, used for exit,
io prio change, etc.

This fixes http://bugzilla.kernel.org/show_bug.cgi?id=9948

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-02-19 10:04:00 +01:00
Jens Axboe fe094d98e7 cfq-iosched: make checkpatch compliant
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-02-01 09:26:33 +01:00
Jens Axboe febffd6181 cfq-iosched: kill some big inlines
Use of inlines were a bit over the top, trim them down a bit.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-01-28 13:19:43 +01:00
Jens Axboe 0871714e08 cfq-iosched: relax IOPRIO_CLASS_IDLE restrictions
Currently you must be root to set idle io prio class on a process. This
is due to the fact that the idle class is implemented as a true idle
class, meaning that it will not make progress if someone else is
requesting disk access. Unfortunately this means that it opens DOS
opportunities by locking down file system resources, hence it is root
only at the moment.

This patch relaxes the idle class a little, by removing the truly idle
part (which entals a grace period with associated timer). The
modifications make the idle class as close to zero impact as can be done
while still guarenteeing progress. This means we can relax the root only
criteria as well.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-01-28 11:38:15 +01:00
Jens Axboe 4ac845a2e9 block: cfq: make the io contect sharing lockless
The io context sharing introduced a per-ioc spinlock, that would protect
the cfq io context lookup. That is a regression from the original, since
we never needed any locking there because the ioc/cic were process private.

The cic lookup is changed from an rbtree construct to a radix tree, which
we can then use RCU to make the reader side lockless. That is the performance
critical path, modifying the radix tree is only done on process creation
(when that process first does IO, actually) and on process exit (if that
process has done IO).

As it so happens, radix trees are also much faster for this type of
lookup where the key is a pointer. It's a very sparse tree.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-01-28 10:50:33 +01:00
Nikanth Karthikesan 66dac98ed0 io_context sharing - cfq changes
changes in the cfq for io_context sharing

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-01-28 10:50:32 +01:00
Jens Axboe fd0928df98 ioprio: move io priority from task_struct to io_context
This is where it belongs and then it doesn't take up space for a
process that doesn't do IO.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-01-28 10:50:29 +01:00
Adrian Bunk 2fdd82bd88 block: let elv_register() return void
elv_register() always returns 0, and there isn't anything it does where
it should return an error (the only error condition is so grave that
it's handled with a BUG_ON).

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-12-18 08:29:28 +01:00
Oleg Nesterov 0e7be9edb9 cfq_idle_class_timer: add paranoid checks for jiffies overflow
In theory, if the queue was idle long enough, cfq_idle_class_timer may have
a false (and very long) timeout because jiffies can wrap into the past wrt
->last_end_request.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-11-07 13:51:35 +01:00
Oleg Nesterov b70c864d3c cfq: fix IOPRIO_CLASS_IDLE delays
After the fresh boot:

	ionice -c3 -p $$
	echo cfq >> /sys/block/XXX/queue/scheduler
	dd if=/dev/XXX of=/dev/null bs=512 count=1

Now dd hangs in D state and the queue is completely stalled for approximately
INITIAL_JIFFIES + CFQ_IDLE_GRACE jiffies. This is because cfq_init_queue()
forgets to initialize cfq_data->last_end_request.

(I guess this patch is not complete, overflow is still possible)

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-11-07 09:46:13 +01:00
Oleg Nesterov 2389d1ef17 cfq: fix IOPRIO_CLASS_IDLE accounting
Spotted by Nick <gentuu@gmail.com>, hopefully can explain the second trace in
http://bugzilla.kernel.org/show_bug.cgi?id=9180.

If ->async_idle_cfqq != NULL cfq_put_async_queues() puts it IOPRIO_BE_NR times
in a loop. Fix this.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-11-07 09:45:00 +01:00
Oleg Nesterov 0a0836a09c cfq_get_queue: fix possible NULL pointer access
cfq_get_queue()->cfq_find_alloc_queue() can fail, check the returned value.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Note that this isn't a bug at the moment, since the regular IO path
does not call this path without __GFP_WAIT set. However, it could be a
future bug, so I've applied it.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-29 11:33:05 +01:00
Oleg Nesterov 4310864b9d cfq_exit_queue() should cancel cfq_data->unplug_work
Spotted by Nick <gentuu@gmail.com>, perhaps explains the first trace in
http://bugzilla.kernel.org/show_bug.cgi?id=9180.

cfq_exit_queue() should cancel cfqd->unplug_work before freeing cfqd.
blk_sync_queue() seems unneeded, removed.

Q: why cfq_exit_queue() calls cfq_shutdown_timer_wq() twice?

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-29 11:33:05 +01:00
Jens Axboe 165125e1e4 [BLOCK] Get rid of request_queue_t typedef
Some of the code has been gradually transitioned to using the proper
struct request_queue, but there's lots left. So do a full sweet of
the kernel and get rid of this typedef and replace its uses with
the proper type.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-24 09:28:11 +02:00
Alexey Dobriyan 8350163a90 cfq: Write-only stuff in CFQ data structures
There are some leftover bits from the task cooperator patch, that was
yanked out again. While it will get reintroduced, no point in having
this write-only stuff in the tree. So yank it.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-20 10:07:50 +02:00
Vasily Tarasov c2dea2d1fd cfq: async queue allocation per priority
If we have two processes with different ioprio_class, but the same
ioprio_data, their async requests will fall into the same queue. I guess
such behavior is not expected, because it's not right to put real-time
requests and best-effort requests in the same queue.

The attached patch fixes the problem by introducing additional *cfqq
fields on cfqd, pointing to per-(class,priority) async queues.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-20 10:06:38 +02:00
Christoph Lameter 94f6030ca7 Slab allocators: Replace explicit zeroing with __GFP_ZERO
kmalloc_node() and kmem_cache_alloc_node() were not available in a zeroing
variant in the past.  But with __GFP_ZERO it is possible now to do zeroing
while allocating.

Use __GFP_ZERO to remove the explicit clearing of memory via memset whereever
we can.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-17 10:23:02 -07:00
Jens Axboe 15c31be4d5 cfq-iosched: fix async queue behaviour
With the cfq_queue hash removal, we inadvertently got rid of the
async queue sharing. This was not intentional, in fact CFQ purposely
shares the async queue per priority level to get good merging for
async writes.

So put some logic in cfq_get_queue() to track the shared queues.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-10 13:43:25 +02:00
Christoph Lameter 0a31bd5f2b KMEM_CACHE(): simplify slab cache creation
This patch provides a new macro

KMEM_CACHE(<struct>, <flags>)

to simplify slab creation. KMEM_CACHE creates a slab with the name of the
struct, with the size of the struct and with the alignment of the struct.
Additional slab flags may be specified if necessary.

Example

struct test_slab {
	int a,b,c;
	struct list_head;
} __cacheline_aligned_in_smp;

test_slab_cache = KMEM_CACHE(test_slab, SLAB_PANIC)

will create a new slab named "test_slab" of the size sizeof(struct
test_slab) and aligned to the alignment of test slab.  If it fails then we
panic.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-07 12:12:55 -07:00
Jens Axboe 597bc485d6 cfq-iosched: speedup cic rb lookup
We often lookup the same queue many times in succession, so cache
the last looked up queue to avoid browsing the rbtree.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:23 +02:00
Vasily Tarasov 91fac317a3 cfq-iosched: get rid of cfqq hash
cfq hash is no more necessary.  We always can get cfqq from io context.
cfq_get_io_context_noalloc() function is introduced, because we don't
want to allocate cic on merging and checking may_queue.  In order to
identify sync queue we've used hash key = CFQ_KEY_ASYNC. Since hash is
eliminated we need to use other criterion: sync flag for queue is added.
In all places where we dig in rb_tree we're in current context, so no
additional locking is required.

Advantages of this patch: no additional memory for hash, no seeking in
hash, code is cleaner. But it is necessary now to seek cic in per-ioc
rbtree, but it is faster:
- most processes work only with few devices
- most systems have only few block devices
- it is a rb-tree

Signed-off-by: Vasily Tarasov <vtaras@openvz.org>

Changes by me:

- Merge into CFQ devel branch
- Get rid of cfq_get_io_context_noalloc()
- Fix various bugs with dereferencing cic->cfqq[] with offset other
  than 0 or 1.
- Fix bug in cfqq setup, is_sync condition was reversed.
- Fix bug where only bio_sync() is used, we need to check for a READ too

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:23 +02:00
Jens Axboe cc19747977 cfq-iosched: tighten queue request overlap condition
For tagged devices, allow overlap of requests if the idle window
isn't enabled on the current active queue.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:23 +02:00
Jens Axboe 3ed9a2965c cfq-iosched: improve sync vs async workloads
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:23 +02:00
Jens Axboe 1be92f2fc7 cfq-iosched: never allow an async queue idling
We don't enable it by default, don't let it get enabled during
runtime.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 20e493a8d0 cfq-iosched: get rid of ->dispatch_slice
We can track it fairly accurately locally, let the slice handling
take care of the rest.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 6084cdda0e cfq-iosched: don't pass unused preemption variable around
We don't use it anymore in the slice expiry handling.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe edd75ffd92 cfq-iosched: get rid of ->cur_rr and ->cfq_list
It's only used for preemption now that the IDLE and RT queues also
use the rbtree. If we pass an 'add_front' variable to
cfq_service_tree_add(), we can set ->rb_key to 0 to force insertion
at the front of the tree.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 67e6b49e39 cfq-iosched: slice offset should take ioprio into account
Use the max_slice-cur_slice as the multipler for the insertion offset.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 498d3aa2b4 [PATCH] cfq-iosched: style cleanups and comments
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 67060e3799 cfq-iosched: sort IDLE queues into the rbtree
Same treatment as the RT conversion, just put the sorted idle
branch at the end of the tree.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe 0c534e0a46 cfq-iosched: sort RT queues into the rbtree
Currently CFQ does a linked insert into the current list for RT
queues. We can just factor the class into the rb insertion,
and then we don't have to treat RT queues in a special way. It's
faster, too.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:22 +02:00
Jens Axboe cc09e2990f [PATCH] cfq-iosched: speed up rbtree handling
For cases where the rbtree is mainly used for sorting and min retrieval,
a nice speedup of the rbtree code is to maintain a cache of the leftmost
node in the tree.

Also spotted in the CFS CPU scheduler code.

Improved by Alan D. Brunelle <Alan.Brunelle@hp.com> by updating the
leftmost hint in cfq_rb_first() if it isn't set, instead of only
updating it on insert.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:21 +02:00
Jens Axboe d9e7620e60 cfq-iosched: rework the whole round-robin list concept
Drawing on some inspiration from the CFS CPU scheduler design, overhaul
the pending cfq_queue concept list management. Currently CFQ uses a
doubly linked list per priority level for sorting and service uses.
Kill those lists and maintain an rbtree of cfq_queue's, sorted by when
to service them.

This unfortunately means that the ionice levels aren't as strong
anymore, will work on improving those later. We only scale the slice
time now, not the number of times we service. This means that latency
is better (for all priority levels), but that the distinction between
the highest and lower levels aren't as big.

The diffstat speaks for itself.

 cfq-iosched.c |  363 +++++++++++++++++---------------------------------
 1 file changed, 125 insertions(+), 238 deletions(-)

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:21 +02:00
Jens Axboe 1afba0451c cfq-iosched: minor updates
- Move the queue_new flag clear to when the queue is selected
- Only select the non-first queue in cfq_get_best_queue(), if there's
  a substantial difference between the best and first.
- Get rid of ->busy_rr
- Only select a close cooperator, if the current queue is known to take
  a while to "think".

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:21 +02:00
Jens Axboe 6d048f5310 cfq-iosched: development update
- Implement logic for detecting cooperating processes, so we
  choose the best available queue whenever possible.

- Improve residual slice time accounting.

- Remove dead code: we no longer see async requests coming in on
  sync queues. That part was removed a long time ago. That means
  that we can also remove the difference between cfq_cfqq_sync()
  and cfq_cfqq_class_sync(), they are now indentical. And we can
  kill the on_dispatch array, just make it a counter.

- Allow a process to go into the current list, if it hasn't been
  serviced in this scheduler tick yet.

Possible future improvements including caching the cfqq lookup
in cfq_close_cooperator(), so we don't have to look it up twice.
cfq_get_best_queue() should just use that last decision instead
of doing it again.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:21 +02:00
Jens Axboe 1e3335de05 cfq-iosched: improve preemption for cooperating tasks
When testing the syslet async io approach, I discovered that CFQ
sometimes didn't perform as well as expected. cfq_should_preempt()
needs to better check for cooperating tasks, so fix that by allowing
preemption of an equal priority queue if the recently queued request
is as good a candidate for IO as the one we are currently waiting for.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-04-30 09:01:21 +02:00
Jens Axboe 5044eed488 cfq-iosched: fix alias + front merge bug
There's a really rare and obscure bug in CFQ, that causes a crash in
cfq_dispatch_insert() due to rq == NULL.  One example of the resulting
oops is seen here:

	http://lkml.org/lkml/2007/4/15/41

Neil correctly diagnosed the situation for how this can happen: if two
concurrent requests with the exact same sector number (due to direct IO
or aliasing between MD and the raw device access), the alias handling
will add the request to the sortlist, but next_rq remains NULL.

Read the more complete analysis at:

	http://lkml.org/lkml/2007/4/25/57

This looks like it requires md to trigger, even though it should
potentially be possible to due with O_DIRECT (at least if you edit the
kernel and doctor some of the unplug calls).

The fix is to move the ->next_rq update to when we add a request to the
rbtree. Then we remove the possibility for a request to exist in the
rbtree code, but not have ->next_rq correctly updated.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-04-25 08:41:48 -07:00
Jens Axboe a993800655 cfq-iosched: fix sequential write regression
We have a 10-15% performance regression for sequential writes on TCQ/NCQ
enabled drives in 2.6.21-rcX after the CFQ update went in.  It has been
reported by Valerie Clement <valerie.clement@bull.net> and the Intel
testing folks.  The regression is because of CFQ's now more aggressive
queue control, limiting the depth available to the device.

This patches fixes that regression by allowing a greater depth when only
one queue is busy.  It has been tested to not impact sync-vs-async
workloads too much - we still do a lot better than 2.6.20.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-04-20 22:56:29 -07:00
Jens Axboe 9ede209e83 cfq-iosched: improve continue or break logic in cfq_dispatch
This improves performance considerably for sync requests when you
have command queuing enabled.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00
Jens Axboe 28f95cbc3e cfq-iosched: remove the implicit queue kicking in slice expire
We only really need it for a process going away, so move it to
those locations.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00
Jens Axboe 3c6bd2f879 cfq-iosched: check whether a queue timed out in accounting
Makes it more fair for the residual slice count.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00
Jens Axboe cb8874119e cfq-iosched: tweak the FIFO checking
We currently check the FIFO once per slice. Optimize that a bit and
only do it as the first thing for a new slice, so we don't end up
doing a single request and then seek to the FIFO requests.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00
Jens Axboe 1792669cc1 cfq-iosched: don't pass in queue for cfq_arm_slice_timer()
It must always be the active queue, otherwise it's a bug. So just
use the active_queue, don't pass it in explicitly.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00
Jens Axboe c5b680f3b7 cfq-iosched: account for slice over/under time
If a slice uses less than it is entitled to (or perhaps more), include
that in the decision on how much time to give it the next time it
gets serviced.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-02-11 23:14:45 +01:00