linux-kernel - Re: [PATCH v5 2/2] x86, mwaitt: introduce mwaix delay with a configurable timer

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Message-ID: <20150615140418.GB28310@hr-slim.amd.com>
Date:	Mon, 15 Jun 2015 22:04:19 +0800
From:	Huang Rui <ray.huang@....com>
To:	Borislav Petkov <bp@...e.de>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Tony Li <tony.li@....com>, Ken Xue <ken.xue@....com>
Subject: Re: [PATCH v5 2/2] x86, mwaitt: introduce mwaix delay with a
 configurable timer

On Mon, Jun 15, 2015 at 01:15:26PM +0200, Borislav Petkov wrote:
> On Mon, Jun 15, 2015 at 12:57:18PM +0200, Peter Zijlstra wrote:
> > Seeing how we disable C states, its unlikely to use less energy, so what
> > exactly is its benefit, other than using fancy new instructions?
> 
> If the "disabling of C states" turns into a "go into a C-state which has
> small wakeup latency" in the future, would be cool. Because we have a
> bunch of places where we do delay.
> 
> Rui, what happens if you enter C1 instead? Any improvements or is the
> wakeup latency too high?
> 

Hmm, the current processor cannot enter C1 with MWAITX, so I don't
confirm if it would have higher wakeup latency on C1 in future.

Thanks,
Rui
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