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Subject[PATCH 4.0 016/220] sched/idle/x86: Optimize unnecessary mwait_idle() resched IPIs
Date
4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Galbraith <bitbucket@online.de>

commit f8e617f4582995f7c25ef25b4167213120ad122b upstream.

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/process.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -429,18 +429,22 @@ static int prefer_mwait_c1_over_halt(con

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)



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