From: Borislav Petkov <bp@alien8.de>
To: Tony Luck <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/cpufeatures: Add feature flag for fast short rep movsb
Date: Thu, 12 Dec 2019 23:52:10 +0100 [thread overview]
Message-ID: <20191212225210.GA22094@zn.tnic> (raw)
In-Reply-To: <20191212214908.20185-1-tony.luck@intel.com>
On Thu, Dec 12, 2019 at 01:49:08PM -0800, Tony Luck wrote:
> From the Intel Optimization Reference Manual:
>
> 3.7.6.1 Fast Short REP MOVSB
> Beginning with processors based on Ice Lake Client microarchitecture,
> REP MOVSB performance of short operations is enhanced. The enhancement
> applies to string lengths between 1 and 128 bytes long. Support for
> fast-short REP MOVSB is enumerated by the CPUID feature flag: CPUID
> [EAX=7H, ECX=0H).EDX.FAST_SHORT_REP_MOVSB[bit 4] = 1. There is no change
> in the REP STOS performance.
>
> Add an X86_FEATURE_FSRM flag for this.
>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>
> Net effect of this patch is just to make "fsrm" appear in the
> flags section of /proc/cpuinfo. Maybe someone can look into whether
> we should make copy routines that use "rep movsb" check for this
> flag to optimize copies on older CPUs that don't have it?
We can then add the feature flag too. Just showing it in /proc/cpuinfo
without any users is kinda pointless...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2019-12-12 22:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-12 21:49 [PATCH] x86/cpufeatures: Add feature flag for fast short rep movsb Tony Luck
2019-12-12 22:52 ` Borislav Petkov [this message]
2019-12-16 21:42 ` [PATCH] x86/cpufeatures: Add support for fast short rep mov Tony Luck
2020-01-07 18:40 ` Borislav Petkov
2020-01-07 22:36 ` Luck, Tony
2020-01-08 10:30 ` Borislav Petkov
2020-01-08 10:38 ` [tip: x86/asm] x86/cpufeatures: Add support for fast short REP; MOVSB tip-bot2 for Tony Luck
2020-01-08 11:54 ` Ingo Molnar
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