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Message-ID: <20121127175023.GI23854@lenny.home.zabbo.net> Date: Tue, 27 Nov 2012 09:50:23 -0800 From: Zach Brown <zab@...bo.net> To: Theodore Ts'o <tytso@....edu> Cc: Ext4 Developers List <linux-ext4@...r.kernel.org> Subject: Re: [PATCH 3/6 -v3] libext2fs: add ext2fs_bitcount() function On Tue, Nov 27, 2012 at 12:16:17AM -0500, Theodore Ts'o wrote: > I did some quick benchmarking, and the difference it makes when > checking 4TB's worth of bitmaps is negligble: > > slow popcount: 0.2623 > fast popcount: 0.0700 > > For a 128TB's worth of bitmaps, the time difference is: > > slow popcount: 8.0185 > fast popcount: 2.2066 > > I measured running e2fsck on an empty 128TB file system, and that took > 202 CPU seconds (assuming all of the fs metadata blocks are in cache), > so with this optimization we would save at most 3%. (For comparison, > using an unmodified 1.42.6 e2fsck, it burned 392.7 CPU seconds.) Nice, thanks for taking the time to get numbers. > My conclusion is that using __builtin_popcnt() is a nice-to-have, and > if someone sends me patches I'll probably take them as a optimization, > but it's not super high priority for me. Agreed. I'll chuck it at the end of my fun-projects-some-day list as well, but getting it right for all the platforms that e2fsprogs supports.. meh :). - z -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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