linux-kernel - Re: [PATCH v5 1/2] x86, mwaitt: add monitorx and mwaitx instruction

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Date:	Mon, 15 Jun 2015 20:42:58 +0800
From:	Huang Rui <ray.huang@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Borislav Petkov <bp@...e.de>,
	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 1/2] x86, mwaitt: add monitorx and mwaitx instruction

On Mon, Jun 15, 2015 at 12:55:42PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 15, 2015 at 06:48:03PM +0800, Huang Rui wrote:
> > +/*
> > + * MWAITT allows for both a timer value to get you out of the MWAIT as
> > + * well as the normal exit conditions.
> > + *
> > + * MWAITX ECX[1]: enable timer if set
> > + * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks
> > + *
> > + * Below is the compared data between MWAIT and MWAITX on AMD
> > + * processors:
> > + *                 MWAIT                           MWAITX
> > + * opcode          0f 01 c9           |            0f 01 fb
> > + * ECX[0]                  value of RFLAGS.IF seen by instruction
> > + * ECX[1]          unused/#GP if set  |            enable timer if set
> > + * ECX[31:2]                     unused/#GP if set
> > + * EAX                           unused (reserve for hint)
> 
> Seeing how you're stuffing a !0 value in here in the next patch, the
> above comment seems slightly incorrect, no?
> 

That's because current processor doesn't support to go C1 state.
The next patch use the hint is to avoid core go to C1 state in future
processor.

Thanks,
Rui
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