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

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Date:	Thu, 21 May 2015 21:30:16 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Borislav Petkov <bp@...e.de>
cc:	Huang Rui <ray.huang@....com>,
	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>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer

On Thu, 21 May 2015, Borislav Petkov wrote:

> On Thu, May 21, 2015 at 10:56:32PM +0800, Huang Rui wrote:
> > Looks like good use case. Boris, could we try to implement it?
> 
> Andy had some suggestions on how to do it here:
> 
> https://lkml.kernel.org/r/555D3629.8080002@kernel.org
> 
> which should be doable. Also, you'd probably need to set ECX[0]=0b too,
> so that MWAITX doesn't get woken up by interrupts while MWAIT-ing with
> interrupts disabled. I.e., this sequence:
> 
> cli
> rdtsc
> shove the computed timeout into ebx
> mov $2,%ecx				# this enables the timer and disables IRQs while MWAITing
> mwaitx
> sti

And the above sucks for udelay, because you disable interrupts for
random amounts of time.

Thanks,

	tglx


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