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

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Date:	Wed, 20 May 2015 13:21:10 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Huang Rui <ray.huang@....com>, Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>, Tony Li <tony.li@....com>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer

On Wed, May 20, 2015 at 01:11:20PM +0200, Ingo Molnar wrote:
>   - MWAITX takes a 'timeout' parameter, but otherwise behaves exactly 
>     like MWAIT: i.e. once idle it won't exit idle on its own

Let me quote the commit message:

"MWAITT, another name is MWAITX (MWAIT with extensions), has a
configurable timer that causes MWAITX to exit on expiration."

You need to set the second bit in ECX to enable the timer.

I guess if you don't, then you get normal MWAIT but then you don't need
the timeout either...

>   - based on the 'timeout' hint, MWAITX can internally optimize how 
>     deep sleep it enters. If the timeout is large it goes deep, if 
>     it's small, it goes shallow.

I haven't heard anything about handling the timeout this way and if it
is not done this way, maybe Rui could forward this idea to hw people...

> If it's a true timeout, as you suggest, then I don't see any obvious
> way to support it, especially if it does not give access to deeper
> sleep states.

Right.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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