linux-kernel - Re: [PATCH v2 2/2] x86/pat: Avoid contention on cpa

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Message-ID: <20120822084702.GA21764@gmail.com>
Date:	Wed, 22 Aug 2012 10:47:02 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Ido Yariv <ido@...ery.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH v2 2/2] x86/pat: Avoid contention on cpa_lock if possible


* Ido Yariv <ido@...ery.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@...lemp.com>.
> 
> Signed-off-by: Ido Yariv <ido@...ery.com>
> Acked-by: Shai Fultheim <shai@...lemp.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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