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SubjectRe: [PATCH REGRESSION FIX] x86 idle: restore mwait_idle()
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On Sat, 2014-01-18 at 10:33 +0100, Mike Galbraith wrote: 
> On Fri, 2014-01-17 at 05:20 +0100, Mike Galbraith wrote:
>
> > taskset 0xc pipe-test 1
> >
> > 3.8.13 3.397977 usecs/loop -- avg 3.400336 588.2 KHz
> > master+ 4.798547 usecs/loop -- avg 4.791692 417.4 KHz
>
> Bah, those are apple/grape, these are apple/apple.

Or, to make it more correct for 3.10..13, add the clflush barriers as
well for afflicted CPUs.

idle: kill unnecessary mwait_idle() resched IPIs

Set/clear polling instead.

Q6600, pipe-test scheduling cross core:
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

Signed-off-by: Mike Galbraith <bitbucket@online.de>
Cc: <stable@vger.kernel.org> # 3.10+
---
arch/x86/kernel/process.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -427,18 +427,21 @@ static int prefer_mwait_c1_over_halt(con

static void mwait_idle(void)
{
- if (!need_resched()) {
- if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+ if (!current_set_polling_and_test()) {
+ if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
+ mb();
clflush((void *)&current_thread_info()->flags);
+ mb();
+ }

__monitor((void *)&current_thread_info()->flags, 0, 0);
- smp_mb();
if (!need_resched())
__sti_mwait(0, 0);
else
local_irq_enable();
} else
local_irq_enable();
+ __current_clr_polling();
}

void select_idle_routine(const struct cpuinfo_x86 *c)



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