From: Andi Kleen <andi@firstfloor.org>
To: ling.ma@intel.com
Cc: mingo@elte.hu, hpa@zytor.com, tglx@linutronix.de,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register
Date: Thu, 11 Oct 2012 06:40:52 -0700 [thread overview]
Message-ID: <m2bog9t9cr.fsf@firstfloor.org> (raw)
In-Reply-To: <1349958548-1868-1-git-send-email-ling.ma@intel.com> (ling ma's message of "Thu, 11 Oct 2012 20:29:08 +0800")
ling.ma@intel.com writes:
> From: Ma Ling <ling.ma@intel.com>
>
> Load and write operation occupy about 35% and 10% respectively
> for most industry benchmarks. Fetched 16-aligned bytes code include
> about 4 instructions, implying 1.34(0.35 * 4) load, 0.4 write.
> Modern CPU support 2 load and 1 write per cycle, so throughput from write is
> bottleneck for memcpy or copy_page, and some slight CPU only support one mem
> operation per cycle. So it is enough to issue one read and write instruction
> per cycle, and we can save registers.
I don't think "saving registers" is a useful goal here.
>
> In this patch we also re-arrange instruction sequence to improve performance
> The performance on atom is improved about 11%, 9% on hot/cold-cache
> case respectively.
That's great, but the question is what happened to the older CPUs that
also this sequence. It may be safer to add a new variant for Atom,
unless you can benchmark those too.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2012-10-11 13:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-11 12:29 [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register ling.ma
2012-10-11 13:40 ` Andi Kleen [this message]
2012-10-12 3:10 ` Ma, Ling
2012-10-12 13:35 ` Andi Kleen
2012-10-12 14:54 ` Ma, Ling
2012-10-12 15:14 ` Andi Kleen
2012-10-11 14:35 ` Konrad Rzeszutek Wilk
2012-10-12 3:37 ` Ma, Ling
2012-10-12 6:18 ` Borislav Petkov
2012-10-12 9:07 ` Ma, Ling
2012-10-12 18:04 ` Borislav Petkov
2012-10-14 10:58 ` Borislav Petkov
2012-10-15 5:00 ` Ma, Ling
2012-10-15 5:13 ` George Spelvin
2012-10-12 21:02 George Spelvin
2012-10-12 23:17 ` Borislav Petkov
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