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SubjectRe: [PATCH v4 2/5] x86/umwait: Initialize umwait control values
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@intel.com>
> Reviewed-by: Ashok Raj <ashok.raj@intel.com>
> Reviewed-by: Andy Lutomirski <luto@kernel.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.

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