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Date: Fri, 12 Aug 2011 11:33:33 -0700 From: Andi Kleen <andi@...stfloor.org> To: melwyn lobo <linux.melwyn@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: x86 memcpy performance melwyn lobo <linux.melwyn@...il.com> writes: > Hi All, > Our Video recorder application uses memcpy for every frame. About 2KB > data every frame on Intel® Atom™ Z5xx processor. > With default 2.6.35 kernel we got 19.6 fps. But it seems kernel > implemented memcpy is suboptimal, because when we replaced > with an optmized one (using ssse3, exact patches are currently being > finalized) ew obtained 22fps a gain of 12.2 %. SSE3 in the kernel memcpy would be incredible expensive, it would need a full FPU saving for every call and preemption disabled. I haven't seen your patches, but until you get all that right (and add a lot more overhead to most copies) you have a good change currently to corrupting user FPU state. > C0 residency also reduced from 75% to 67%. This means power benefits too. > My questions: > 1. Is kernel memcpy profiled for optimal performance. It depends on the CPU There have been some improvements for Atom on newer kernels I believe. But then kernel memcpy is usually optimized for relatively small copies (<= 4K) because very few kernel loads do more. -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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