linux-kernel - Re: [tip:x86/idle] x86, acpi, idle: Restructure the mwait idle routines

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Message-ID: <20131219201634.GR16438@laptop.programming.kicks-ass.net>
Date:	Thu, 19 Dec 2013 21:16:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	arjan@...ux.intel.com, rui.zhang@...el.com, bitbucket@...ine.de,
	rafael.j.wysocki@...el.com, lenb@...nel.org, tglx@...utronix.de,
	jacob.jun.pan@...ux.intel.com, hpa@...ux.intel.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/idle] x86, acpi, idle: Restructure the mwait idle
 routines

On Thu, Dec 19, 2013 at 12:13:29PM -0800, H. Peter Anvin wrote:
> On 12/19/2013 12:09 PM, tip-bot for Peter Zijlstra wrote:
> > diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
> > index 8f181b3..e8275f2 100644
> > --- a/drivers/thermal/intel_powerclamp.c
> > +++ b/drivers/thermal/intel_powerclamp.c
> > @@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
> >  			 */
> >  			local_touch_nmi();
> >  			stop_critical_timings();
> > -			__monitor((void *)&current_thread_info()->flags, 0, 0);
> > -			cpu_relax(); /* allow HT sibling to run */
> > -			__mwait(eax, ecx);
> > +			mwait_idle_with_hints(eax, ecx);
> >  			start_critical_timings();
> >  			atomic_inc(&idle_wakeup_counter);
> >  		}
> > 
> 
> Should this cpu_relax() be in the common code as well?

I don't think so; it seems weird to allow a sibling some time between
monitor and wait because the moment wait stalls the cpu the sibling gets
all the time it wants.
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