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

[Fenghua Yu]

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@xxxxxxxxx>
> > Reviewed-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> > Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > ---
> >  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