linux-kernel - Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a configurable timer

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Message-ID: <20150521145632.GC22642@hr-slim.amd.com>
Date:	Thu, 21 May 2015 22:56:32 +0800
From:	Huang Rui <ray.huang@....com>
To:	Borislav Petkov <bp@...e.de>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>, Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	"Aaron Lu" <aaron.lu@...el.com>, "Li, Tony" <Tony.Li@....com>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer

On Thu, May 21, 2015 at 04:15:54AM +0800, Borislav Petkov wrote:
> On Wed, May 20, 2015 at 09:12:15PM +0200, Thomas Gleixner wrote:
> > Which would be good enough for mdelay/udelay I think, but we'd need to
> > measure the time spend in MWAITT so we wont return early.
> > 
> > Something like this:
> 
> Yeah, with a check maybe:
> 
> > 	  delay = usec_to_tsc(delay_usec);
> 
> 	if (delay > ((1 << 32) - 1)) {
> 		mdelay(delay_usec);
> 		return;
> 	}
> 
> > 	  end = rdtsc() + delay;
> > 	  while (1) {
> 
> I guess
> 		monitorx( ...);
> 
> first.
> 
> > 		MWAITT(delay);
> > 		now = rdtsc();
> > 		if (end <= now)
> > 		   	  break;
> > 		delay = end - now;
> > 	}
> > 
> > Now we'd need to add alternatives or some other mechanism to it to
> > make this conditionally for those machines.
> 
> alternative_call(mdelay, mdelayx, X86_FEATURE_MWAITT, /* no output */, timeout);
> 
> Something like that maybe.
> 
> > Not sure if it's worth the trouble.
> 
> Could be a use case for MWAITX in the kernel!
> 

Looks like good use case. Boris, could we try to implement it?

Thanks,
Rui
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