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SubjectRe: [PATCH v2 2/2] x86/pat: Avoid contention on cpa_lock if possible

* Ido Yariv <ido@wizery.com> wrote:

> vSMP Foundation does not require to serialize CPA by guaranteeing that
> the most recent TLB entry will always be used.
>
> To avoid needless contention on cpa_lock, do not lock/unlock it if it
> isn't necessary.
>
> Based on work by Shai Fultheim <shai@scalemp.com>.
>
> Signed-off-by: Ido Yariv <ido@wizery.com>
> Acked-by: Shai Fultheim <shai@scalemp.com>
> ---
> Changes from v1:
> - Use a synthetic CPUID bit and a use static_cpu_has() as suggested by
> H. Peter Avnin
>
> arch/x86/include/asm/cpufeature.h | 1 +
> arch/x86/kernel/vsmp_64.c | 10 ++++++++++
> arch/x86/mm/pageattr.c | 30 +++++++++++++++++++++---------
> 3 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 6b7ee5f..92303a0 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -97,6 +97,7 @@
> #define X86_FEATURE_EXTD_APICID (3*32+26) /* has extended APICID (8 bits) */
> #define X86_FEATURE_AMD_DCM (3*32+27) /* multi-node processor */
> #define X86_FEATURE_APERFMPERF (3*32+28) /* APERFMPERF */
> +#define X86_FEATURE_NO_CPA_LOCK (3*32+29) /* Serializing cpa is not required */

Patch looks mostly good, but could we please use some more
hardware-ish name, instead of referring to a kernel lock?

I.e. how would you name it if this was a real hardware feature?
Certainly not 'No CPA Lock'.

Thanks,

Ingo


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