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Date: Thu, 14 May 2009 19:29:01 +0200 From: Andi Kleen <andi@...stfloor.org> To: Ulrich Drepper <drepper@...il.com> Cc: Andi Kleen <andi@...stfloor.org>, Harvey Harrison <harvey.harrison@...il.com>, Tobias Doerffel <tobias.doerffel@...il.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: Specific support for Intel Atom architecture On Thu, May 14, 2009 at 09:19:38AM -0700, Ulrich Drepper wrote: > On Thu, May 14, 2009 at 7:01 AM, Andi Kleen <andi@...stfloor.org> wrote: > > How would you test that? > > Compare runtimes with mov+bswap for some simple code which uses the > value after the conversion (e.g., just add to something). > > Or in your case: get the Atom designers to comment. Don't really need Atom designers; you can prove or disprove my theory (that they generate the same uops sequence) by checking the uops performance counter for a micro benchmark. However even if that was not the case I have some doubts the kernel is doing enough endian conversions that it really matters. For example the network stack is doing maybe 4-5 endian conversions (very conservative estimate) per packet and processing a packet takes tens of thousands of cycles. But at best you could save 1-2 cycles this way, so even if you save a few cycles this way it will be very likely in the noise. -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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