linux-kernel - Re: [PATCH] x86 idle: repair large-server 50-watt idle-power regression

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Message-ID: <20131219160210.GA28426@gmail.com>
Date:	Thu, 19 Dec 2013 17:02:10 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Len Brown <lenb@...nel.org>, x86@...nel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Len Brown <len.brown@...el.com>, stable@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power
 regression


* H. Peter Anvin <hpa@...or.com> wrote:

> On 12/19/2013 04:22 AM, Ingo Molnar wrote:
> >> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> >> index 92d1206..f80b700 100644
> >> --- a/drivers/idle/intel_idle.c
> >> +++ b/drivers/idle/intel_idle.c
> >> @@ -377,6 +377,9 @@ static int intel_idle(struct cpuidle_device *dev,
> >>  
> >>  	if (!current_set_polling_and_test()) {
> >>  
> >> +		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
> >> +			clflush((void *)&current_thread_info()->flags);
> >> +
> >>  		__monitor((void *)&current_thread_info()->flags, 0, 0);
> > 
> > I don't think either of these casts to '(void *)' is needed, both the 
> > clflush() and __monitor() will take pointers.
> 
> __monitor() currently doesn't, which is idiotic.

Hm, __monitor() seems to take a void *:

 arch/x86/include/asm/processor.h:static inline void __monitor(const void *eax, unsigned long ecx,

So writing:

		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
			clflush(&current_thread_info()->flags);

  		__monitor(&current_thread_info()->flags, 0, 0);

ought to work just fine.

Thanks,

	Ingo
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