linux-kernel - Re: [PATCH RFC] [X86] performance improvement for memcpy

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Message-ID: <20091019071740.GA17407@elte.hu>
Date:	Mon, 19 Oct 2009 09:17:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	linguranus@...il.com, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
	avoid memory miss predication.


* linguranus@...il.com <linguranus@...il.com> wrote:

> From: Ling <linguranus@...il.com>
> 
> Hi All
> 
> CPU will use memory disambiguration predication to speculatively read 
> memory without waiting for previous write instructions and correctly 
> avoid conflict between them (RAW). However it seem only to care about 
> last 12 bits of address, not care about real address. For example if 
> rsi is 0xf004, rdi is 0xe008, when we do following operation there 
> will generate big performance latency.

Would be nice to trigger this kind of pattern via some testcase that 
uses read() or write() - or some other real workload.

Then you can use 'perf stat --repeat 10 ./my-test-prog' to measure it 
and post the results - the before-patch/after-patch instruction count, 
cycle count, etc.

You can get 'perf' via:

  cd tools/perf
  make -j install

(And please preserve the Cc: line for new postings - thanks.)

Thanks,

	Ingo
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