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sched: Move the second half of ttwu() to the remote cpu

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Now that we've removed the rq->lock requirement from the first part of
ttwu() and can compute placement without holding any rq->lock, ensure
we execute the second half of ttwu() on the actual cpu we want the
task to run on.

This avoids having to take rq->lock and doing the task enqueue
remotely, saving lots on cacheline transfers.

As measured using: http://oss.oracle.com/~mason/sembench.c

  $ for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance > $i; done
  $ echo 4096 32000 64 128 > /proc/sys/kernel/sem
  $ ./sembench -t 2048 -w 1900 -o 0

  unpatched: run time 30 seconds 647278 worker burns per second
  patched:   run time 30 seconds 816715 worker burns per second

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110405152729.515897185@chello.nl
This commit is contained in:
Peter Zijlstra
2011-04-05 17:23:58 +02:00
committed by Ingo Molnar
parent c05fbafba1
commit 317f394160
4 changed files with 69 additions and 1 deletions
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3
include/linux/sched.h
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@ -1203,6 +1203,7 @@ struct task_struct {
int lock_depth; /* BKL lock depth */
#ifdef CONFIG_SMP
struct task_struct *wake_entry;
int on_cpu;
#endif
int on_rq;
@ -2192,7 +2193,7 @@ extern void set_task_comm(struct task_struct *tsk, char *from);
extern char *get_task_comm(char *to, struct task_struct *tsk);
#ifdef CONFIG_SMP
static inline void scheduler_ipi(void) { }
void scheduler_ipi(void);
extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
#else
static inline void scheduler_ipi(void) { }