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2011-08-14sched/cpupri: Remove cpupri->pri_activeYong Zhang1-2/+1
Since [sched/cpupri: Remove the vec->lock], member pri_active of struct cpupri is not needed any more, just remove it. Also clean stuff related to it. Signed-off-by: Yong Zhang <yong.zhang0@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/20110806001004.GA2207@zhy Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-08-14sched/cpupri: Fix memory barriers for vec updates to always be in orderSteven Rostedt1-3/+25
[ This patch actually compiles. Thanks to Mike Galbraith for pointing that out. I compiled and booted this patch with no issues. ] Re-examining the cpupri patch, I see there's a possible race because the update of the two priorities vec->counts are not protected by a memory barrier. When a RT runqueue is overloaded and wants to push an RT task to another runqueue, it scans the RT priority vectors in a loop from lowest priority to highest. When we queue or dequeue an RT task that changes a runqueue's highest priority task, we update the vectors to show that a runqueue is rated at a different priority. To do this, we first set the new priority mask, and increment the vec->count, and then set the old priority mask by decrementing the vec->count. If we are lowering the runqueue's RT priority rating, it will trigger a RT pull, and we do not care if we miss pushing to this runqueue or not. But if we raise the priority, but the priority is still lower than an RT task that is looking to be pushed, we must make sure that this runqueue is still seen by the push algorithm (the loop). Because the loop reads from lowest to highest, and the new priority is set before the old one is cleared, we will either see the new or old priority set and the vector will be checked. But! Since there's no memory barrier between the updates of the two, the old count may be decremented first before the new count is incremented. This means the loop may see the old count of zero and skip it, and also the new count of zero before it was updated. A possible runqueue that the RT task could move to could be missed. A conditional memory barrier is placed between the vec->count updates and is only called when both updates are done. The smp_wmb() has also been changed to smp_mb__before_atomic_inc/dec(), as they are not needed by archs that already synchronize atomic_inc/dec(). The smp_rmb() has been moved to be called at every iteration of the loop so that the race between seeing the two updates is visible by each iteration of the loop, as an arch is free to optimize the reading of memory of the counters in the loop. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1312547269.18583.194.camel@gandalf.stny.rr.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-08-14sched/cpupri: Remove the vec->lockSteven Rostedt1-23/+39
sched/cpupri: Remove the vec->lock The cpupri vec->lock has been showing up as a top contention lately. This is because of the RT push/pull logic takes an agressive approach for migrating RT tasks. The cpupri logic is in place to improve the performance of the push/pull when dealing with large number CPU machines. The problem though is a vec->lock is required, where a vec is a global per RT priority structure. That is, if there are lots of RT tasks at the same priority, every time they are added or removed from the RT queue, this global vec->lock is taken. Now that more kernel threads are becoming RT (RCU boost and threaded interrupts) this is becoming much more of an issue. There are two variables that are being synced by the vec->lock. The cpupri bitmask, and the vec->counter. The cpupri bitmask is one bit per priority. If a RT priority vec has a process queued, then the vec->count is > 0 and the cpupri bitmask is set for that RT priority. If the cpupri bitmask gets out of sync with the vec->counter, we could end up pushing a low proirity RT task to a high priority queue. That RT task that could have run immediately could be queued on a run queue with a higher priority task indefinitely. The solution is not to use the cpupri bitmask and just look at the vec->count directly when doing a pull. The cpupri bitmask is just a fast way to scan the RT priorities when a pull is made. Instead of using the bitmask, and just examine all RT priorities, and look at the vec->counts, we could eliminate the vec->lock. The scan of RT tasks is to find a run queue that we can push an RT task to, and we do not push to a high priority queue, thus the scan only needs to go from 1 to RT task->prio, and not all 100 RT priorities. The push algorithm, which does the scan of RT priorities (and scan of the bitmask) only happens when we have an overloaded RT run queue (more than one RT task queued). The grabbing of the vec->lock happens every time any RT task is queued or dequeued on the run queue for that priority. The slowing down of the scan by not using a bitmask is negligible by the speed up of removing the vec->lock contention, and replacing it with an atomic counter and memory barrier. To prove this, I wrote a patch that times both the loop and the code that grabs the vec->locks. I passed the patches to various people (and companies) to test and show the results. I let everyone choose their own load to test, giving different loads on the system, for various different setups. Here's some of the results: (snipping to a few CPUs to not make this change log huge, but the results were consistent across the entire system). System 1 (24 CPUs) Before patch: CPU: Name Count Max Min Average Total ---- ---- ----- --- --- ------- ----- [...] cpu 20: loop 3057 1.766 0.061 0.642 1963.170 vec 6782949 90.469 0.089 0.414 2811760.503 cpu 21: loop 2617 1.723 0.062 0.641 1679.074 vec 6782810 90.499 0.089 0.291 1978499.900 cpu 22: loop 2212 1.863 0.063 0.699 1547.160 vec 6767244 85.685 0.089 0.435 2949676.898 cpu 23: loop 2320 2.013 0.062 0.594 1380.265 vec 6781694 87.923 0.088 0.431 2928538.224 After patch: cpu 20: loop 2078 1.579 0.061 0.533 1108.006 vec 6164555 5.704 0.060 0.143 885185.809 cpu 21: loop 2268 1.712 0.065 0.575 1305.248 vec 6153376 5.558 0.060 0.187 1154960.469 cpu 22: loop 1542 1.639 0.095 0.533 823.249 vec 6156510 5.720 0.060 0.190 1172727.232 cpu 23: loop 1650 1.733 0.068 0.545 900.781 vec 6170784 5.533 0.060 0.167 1034287.953 All times are in microseconds. The 'loop' is the amount of time spent doing the loop across the priorities (before patch uses bitmask). the 'vec' is the amount of time in the code that requires grabbing the vec->lock. The second patch just does not have the vec lock, but encompasses the same code. Amazingly the loop code even went down on average. The vec code went from .5 down to .18, that's more than half the time spent! Note, more than one test was run, but they all had the same results. System 2 (64 CPUs) Before patch: CPU: Name Count Max Min Average Total ---- ---- ----- --- --- ------- ----- cpu 60: loop 0 0 0 0 0 vec 5410840 277.954 0.084 0.782 4232895.727 cpu 61: loop 0 0 0 0 0 vec 4915648 188.399 0.084 0.570 2803220.301 cpu 62: loop 0 0 0 0 0 vec 5356076 276.417 0.085 0.786 4214544.548 cpu 63: loop 0 0 0 0 0 vec 4891837 170.531 0.085 0.799 3910948.833 After patch: cpu 60: loop 0 0 0 0 0 vec 5365118 5.080 0.021 0.063 340490.267 cpu 61: loop 0 0 0 0 0 vec 4898590 1.757 0.019 0.071 347903.615 cpu 62: loop 0 0 0 0 0 vec 5737130 3.067 0.021 0.119 687108.734 cpu 63: loop 0 0 0 0 0 vec 4903228 1.822 0.021 0.071 348506.477 The test run during the measurement did not have any (very few, from other CPUs) RT tasks pushing. But this shows that it helped out tremendously with the contention, as the contention happens because the vec->lock is taken only on queuing at an RT priority, and different CPUs that queue tasks at the same priority will have contention. I tested on my own 4 CPU machine with the following results: Before patch: CPU: Name Count Max Min Average Total ---- ---- ----- --- --- ------- ----- cpu 0: loop 2377 1.489 0.158 0.588 1398.395 vec 4484 770.146 2.301 4.396 19711.755 cpu 1: loop 2169 1.962 0.160 0.576 1250.110 vec 4425 152.769 2.297 4.030 17834.228 cpu 2: loop 2324 1.749 0.155 0.559 1299.799 vec 4368 779.632 2.325 4.665 20379.268 cpu 3: loop 2325 1.629 0.157 0.561 1306.113 vec 4650 408.782 2.394 4.348 20222.577 After patch: CPU: Name Count Max Min Average Total ---- ---- ----- --- --- ------- ----- cpu 0: loop 2121 1.616 0.113 0.636 1349.189 vec 4303 1.151 0.225 0.421 1811.966 cpu 1: loop 2130 1.638 0.178 0.644 1372.927 vec 4627 1.379 0.235 0.428 1983.648 cpu 2: loop 2056 1.464 0.165 0.637 1310.141 vec 4471 1.311 0.217 0.433 1937.927 cpu 3: loop 2154 1.481 0.162 0.601 1295.083 vec 4236 1.253 0.230 0.425 1803.008 This was running my migrate.c code that can be found at: http://lwn.net/Articles/425763/ The migrate code does stress the RT tasks a bit. This shows that the loop did increase a little after the patch, but not by much. The vec code dropped dramatically. From 4.3us down to .42us. That's a 10x improvement! Tested-by: Mike Galbraith <mgalbraith@suse.de> Tested-by: Luis Claudio R. Gonçalves <lgoncalv@redhat.com> Tested-by: Matthew Hank Sabins<msabins@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Gregory Haskins <gregory.haskins@gmail.com> Acked-by: Hillf Danton <dhillf@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Chris Mason <chris.mason@oracle.com> Link: http://lkml.kernel.org/r/1312317372.18583.101.camel@gandalf.stny.rr.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-07-17sched: No need for bootmem special casesPekka Enberg1-6/+2
As of commit dcce284 ("mm: Extend gfp masking to the page allocator") and commit 7e85ee0 ("slab,slub: don't enable interrupts during early boot"), the slab allocator makes sure we don't attempt to sleep during boot. Therefore, remove bootmem special cases from the scheduler and use plain GFP_KERNEL instead. Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1279225102-2572-1-git-send-email-penberg@cs.helsinki.fi> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-03-30include cleanup: Update gfp.h and slab.h includes to prepare for breaking ↵Tejun Heo1-0/+1
implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-08Merge branch 'for-next' into for-linusJiri Kosina1-1/+1
Conflicts: Documentation/filesystems/proc.txt arch/arm/mach-u300/include/mach/debug-macro.S drivers/net/qlge/qlge_ethtool.c drivers/net/qlge/qlge_main.c drivers/net/typhoon.c
2010-03-06bitops: rename for_each_bit() to for_each_set_bit()Akinobu Mita1-1/+1
Rename for_each_bit to for_each_set_bit in the kernel source tree. To permit for_each_clear_bit(), should that ever be added. The patch includes a macro to map the old for_each_bit() onto the new for_each_set_bit(). This is a (very) temporary thing to ease the migration. [akpm@linux-foundation.org: add temporary for_each_bit()] Suggested-by: Alexey Dobriyan <adobriyan@gmail.com> Suggested-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Russell King <rmk@arm.linux.org.uk> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Artem Bityutskiy <dedekind@infradead.org> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-02-04Fix misspellings of "invocation" in comments.Adam Buchbinder1-1/+1
Some comments misspell "invocation"; this fixes them. No code changes. Signed-off-by: Adam Buchbinder <adam.buchbinder@gmail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2010-02-02sched: Use for_each_bitAkinobu Mita1-3/+1
No change in functionality. Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> LKML-Reference: <1264938810-4173-1-git-send-email-akinobu.mita@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-12-14sched: Convert cpupri lock to raw_spinlockThomas Gleixner1-5/+5
Convert locks which cannot be sleeping locks in preempt-rt to raw_spinlocks. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Add new prio to cpupri before removing old prioSteven Rostedt1-14/+16
We need to add the new prio to the cpupri accounting before removing the old prio. This is because removing the old prio first will open a race window where the cpu will be removed from pri_active. In this case the cpu will not be visible for RT push and pulls. This could cause a RT task to not migrate appropriately, and create a very large latency. This bug was found with the use of ftrace sched events and trace_printk. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090729042526.438281019@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Fix race in cpupri introduced by cpumask_var changesGregory Haskins1-1/+14
Background: Several race conditions in the scheduler have cropped up recently, which Steven and I have tracked down using ftrace. The most recent one turns out to be a race in how the scheduler determines a suitable migration target for RT tasks, introduced recently with commit: commit 68e74568fbe5854952355e942acca51f138096d9 Date: Tue Nov 25 02:35:13 2008 +1030 sched: convert struct cpupri_vec cpumask_var_t. The original design of cpupri allowed lockless readers to quickly determine a best-estimate target. Races between the pri_active bitmap and the vec->mask were handled in the original code because we would detect and return "0" when this occured. The design was predicated on the *effective* atomicity (*) of caching the result of cpus_and() between the cpus_allowed and the vec->mask. Commit 68e74568 changed the behavior such that vec->mask is accessed multiple times. This introduces a subtle race, the result of which means we can have a result that returns "1", but with an empty bitmap. *) yes, we know cpus_and() is not a locked operator across the entire composite array, but it is implicitly atomic on a per-word basis which is all the design required to work. Implementation: Rather than forgoing the lockless design, or reverting to a stack-based cpumask_t, we simply check for when the race has been encountered and continue processing in the event that the race is hit. This renders the removal race as if the priority bit had been atomically cleared as well, and allows the algorithm to execute correctly. Signed-off-by: Gregory Haskins <ghaskins@novell.com> CC: Rusty Russell <rusty@rustcorp.com.au> CC: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090730145728.25226.92769.stgit@dev.haskins.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-06-17sched: Remove unneeded __ref tagLi Zefan1-1/+1
Those two functions no longer call alloc_bootmmem_cpumask_var(), so no need to tag them with __init_refok. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Pekka Enberg <penberg@cs.helsinki.fi> LKML-Reference: <4A35DD5B.9050106@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-06-11sched: use slab in cpupri_init()Pekka Enberg1-3/+5
Lets not use the bootmem allocator in cpupri_init() as slab is already up when it is run. Cc: Ingo Molnar <mingo@elte.hu> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Yinghai Lu <yinghai@kernel.org> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
2009-06-09cpumask: alloc zeroed cpumask for static cpumask_var_tsYinghai Lu1-1/+1
These are defined as static cpumask_var_t so if MAXSMP is not used, they are cleared already. Avoid surprises when MAXSMP is enabled. Signed-off-by: Yinghai Lu <yinghai.lu@kernel.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2009-04-01sched_rt: don't allocate cpumask in fastpathRusty Russell1-2/+3
Impact: cleanup As pointed out by Steven Rostedt. Since the arg in question is unused, we simply change cpupri_find() to accept NULL. Reported-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> LKML-Reference: <200903251501.22664.rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-06sched: fix section mismatchLi Zefan1-1/+1
init_rootdomain() calls alloc_bootmem_cpumask_var() at system boot, so does cpupri_init(). Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-11-24sched: convert struct cpupri_vec cpumask_var_t.Rusty Russell1-11/+28
Impact: stack usage reduction, (future) size reduction for large NR_CPUS. Dynamically allocating cpumasks (when CONFIG_CPUMASK_OFFSTACK) saves space for small nr_cpu_ids but big CONFIG_NR_CPUS. The fact cpupro_init is called both before and after the slab is available makes for an ugly parameter unfortunately. We also use cpumask_any_and to get rid of a temporary in cpupri_find. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-06sched: use a 2-d bitmap for searching lowest-pri CPUGregory Haskins1-0/+174
The current code use a linear algorithm which causes scaling issues on larger SMP machines. This patch replaces that algorithm with a 2-dimensional bitmap to reduce latencies in the wake-up path. Signed-off-by: Gregory Haskins <ghaskins@novell.com> Acked-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>