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Message-ID: <20150519094253.GA11328@hr-slim.amd.com>
Date: Tue, 19 May 2015 17:42:54 +0800
From: Huang Rui <ray.huang@....com>
To: Borislav Petkov <bp@...en8.de>
CC: Len Brown <lenb@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
"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>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Mwait usage on AMD processors
On Tue, May 19, 2015 at 04:50:17PM +0800, Borislav Petkov wrote:
> On Tue, May 19, 2015 at 03:25:53PM +0800, Huang Rui wrote:
> > Apology that cause to misunderstand. It's not as same as intel.
> > Intel is able to go to C1E like you said, the C1E has less power
> > consumption than C1 on Intel platform.
>
> You still misunderstand - I'm not talking about Intel platforms here but
> AMD ones. On AMD we never enter idle with MWAIT - we do HLT which enters
> C1 and then the hw enters C1E when a bunch of conditions are fulfilled.
>
OK, got it. I see on AMD platforms, we all use default_idle (HLT).
> > The faster waiting exit speed. But it's hard to test the improvement,
> > do you have any idea? It's told by HW designer.
>
> You can test the improvement with a special setup only. Unless you can
> read out power consumption of a box while it is idle.
>
Could you please explain how to create the "special setup"? Actually,
that's my difficulty.
> The exit-idle speed only does not suffice to switch to MWAIT though,
> IMHO. I think power consumption in idle should be the relevant metric
> here.
>
Yes, I agree with you. So that's why I was asking to provide an
optional parameter, not set it default.
> > Current CPU, power consumption cannot go to deeper low power state
> > (C1) via mwaitx/mwait. But HW designers will implement it in future
> > processors.
>
> So future CPUs we will switch to MWAIT. I don't see a problem with that.
>
Yes, at that time, we would like to use mwaitx/mwait as default idle
routine for AMD.
Thanks,
Rui
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