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sched/idle/x86: Optimize unnecessary mwait_idle() resched IPIs 

To fully take advantage of MWAIT, apparently the CLFLUSH instruction needs
another quirk on certain CPUs: proper barriers around it on certain machines.

On a Q6600 SMP system, pipe-test scheduling performance, cross core,
improves significantly:

  3.8.13                   487.2 KHz    1.000
  3.13.0-master            415.5 KHz     .852
  3.13.0-master+           415.2 KHz     .852     + restore mwait_idle
  3.13.0-master++          488.5 KHz    1.002     + restore mwait_idle + IPI fix

Since X86_BUG_CLFLUSH_MONITOR is already a quirk, don't create a separate
quirk for the extra smp_mb()s.

Signed-off-by: Mike Galbraith <bitbucket@online.de>
Cc: <stable@vger.kernel.org> # 3.10+
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ian Malone <ibmalone@gmail.com>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1390061684.5566.4.camel@marge.simpson.net
[ Ported to recent kernel, added comments about the quirk. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mike Galbraith 2014-01-18 17:14:44 +01:00 committed by Ingo Molnar
parent b253149b84
commit f8e617f458
1 changed files with 8 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/kernel/process.c
View File

@ -428,18 +428,22 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
static void mwait_idle(void)
{
if (!need_resched()) {
if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR))
if (!current_set_polling_and_test()) {
if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) {
smp_mb(); /* quirk */
clflush((void *)&current_thread_info()->flags);
smp_mb(); /* quirk */
}
__monitor((void *)&current_thread_info()->flags, 0, 0);
smp_mb();
if (!need_resched())
__sti_mwait(0, 0);
else
local_irq_enable();
} else
} else {
local_irq_enable();
}
__current_clr_polling();
}
void select_idle_routine(const struct cpuinfo_x86 *c)