Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by fast string.

From: "H. Peter Anvin" <hpa@zytor.com>
To: ling.ma@intel.com
Cc: mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by fast string.
Date: Fri, 06 Nov 2009 11:26:04 -0800	[thread overview]
Message-ID: <4AF4784C.5090800@zytor.com> (raw)
In-Reply-To: <4AF457E0.4040107@zytor.com>

On 11/06/2009 09:07 AM, H. Peter Anvin wrote:
> 
> Where did the 1024 byte threshold come from?  It seems a bit high to me,
> and is at the very best a CPU-specific tuning factor.
> 
> Andi is of course correct that older CPUs might suffer (sadly enough),
> which is why we'd at the very least need some idea of what the
> performance impact on those older CPUs would look like -- at that point
> we can make a decision to just unconditionally do the rep movs or
> consider some system where we point at different implementations for
> different processors -- memcpy is probably one of the very few
> operations for which something like that would make sense.
> 

To be expicit: Ling, would you be willing to run some benchmarks across
processors to see how this performs on non-Nehalem CPUs?

	-hpa