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Message-ID: <m2bog9t9cr.fsf@firstfloor.org> Date: Thu, 11 Oct 2012 06:40:52 -0700 From: Andi Kleen <andi@...stfloor.org> To: ling.ma@...el.com Cc: mingo@...e.hu, hpa@...or.com, tglx@...utronix.de, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register ling.ma@...el.com writes: > From: Ma Ling <ling.ma@...el.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@...ux.intel.com -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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