linux-kernel - Re: [PATCH v2 8/8 only] x86,vdso: Use LSL unconditionally for vgetcpu

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Date:	Mon, 27 Oct 2014 04:31:02 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 8/8 only] x86,vdso: Use LSL unconditionally for vgetcpu

Andy Lutomirski <luto@...capital.net> writes:

> LSL is faster than RDTSCP and works everywhere; there's no need to
> switch between them depending on CPU.

Yes it should have been done like this from day 1.

> diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
> index 9793322751e0..d14bb8faad16 100644
> --- a/arch/x86/vdso/vclock_gettime.c
> +++ b/arch/x86/vdso/vclock_gettime.c
> @@ -11,6 +11,9 @@
>   * Check with readelf after changing.
>   */
>  
> +/* Disable static_cpu_has debugging; it doesn't work in the vDSO */
> +#undef CONFIG_X86_DEBUG_STATIC_CPU_HAS
> +
>  #include <uapi/linux/time.h>
>  #include <asm/vgtod.h>
>  #include <asm/hpet.h>
> diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c
> index add1d98d2477..fd8470c98ab5 100644
> --- a/arch/x86/vdso/vgetcpu.c
> +++ b/arch/x86/vdso/vgetcpu.c
> @@ -5,10 +5,12 @@
>   * Fast user context implementation of getcpu()
>   */
>  
> +/* Disable static_cpu_has debugging; it doesn't work in the vDSO */
> +#undef CONFIG_X86_DEBUG_STATIC_CPU_HAS


These two hunks are unrelated?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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