linux-kernel - Re: [PATCH v4 2/5] x86/umwait: Initialize umwait control values

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Date:   Tue, 11 Jun 2019 10:04:02 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v4 2/5] x86/umwait: Initialize umwait control values

On Tue, Jun 11, 2019 at 10:50:36AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 07, 2019 at 03:00:34PM -0700, Fenghua Yu wrote:
> > umwait or tpause allows processor to enter a light-weight
> > power/performance optimized state (C0.1 state) or an improved
> > power/performance optimized state (C0.2 state) for a period
> > specified by the instruction or until the system time limit or until
> > a store to the monitored address range in umwait.
> > 
> > IA32_UMWAIT_CONTROL MSR register allows kernel to enable/disable C0.2
> > on the processor and set maximum time the processor can reside in
> > C0.1 or C0.2.
> > 
> > By default C0.2 is enabled so the user wait instructions can enter the
> > C0.2 state to save more power with slower wakeup time.
> > 
> > Default maximum umwait time is 100000 cycles. A later patch provides
> > a sysfs interface to adjust this value.
> > 
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> > Reviewed-by: Ashok Raj <ashok.raj@...el.com>
> > Reviewed-by: Andy Lutomirski <luto@...nel.org>
> > ---
> >  arch/x86/include/asm/msr-index.h |  4 +++
> >  arch/x86/power/Makefile          |  1 +
> >  arch/x86/power/umwait.c          | 56 ++++++++++++++++++++++++++++++++
> 
> Why is this in power/, this isn't in the least related to
> suspend/hybernate. arch/x86/kernel/cpu/ might be a better place for
> instruction support.

Ok. I can move umwait.c to arch/x86/kernel/cpu/umwait.c.

Thanks.

-Fenghua