On Thu, Dec 01, 2011 at 12:13:41PM -0800, Darrick J. Wong wrote: > Hi all, > > This patchset (re)uses Bob Pearson's crc32 slice-by-8 code to stamp out a > software crc32c implementation. It removes the crc32c implementation in > crypto/ in favor of using the stamped-out one in lib/. There is also a change > to Kconfig so that the kernel builder can pick an implementation best suited > for the hardware. > > The motivation for this patchset is that I am working on adding full metadata > checksumming to ext4. As far as performance impact of adding checksumming > goes, I see nearly no change with a standard mail server ffsb simulation. On a > test that involves only file creation and deletion and extent tree writes, I > see a drop of about 50 pcercent with the current kernel crc32c implementation; > this improves to a drop of about 20 percent with the enclosed crc32c code. > > When metadata is usually a small fraction of total IO, this new implementation > doesn't help much because metadata is usually a small fraction of total IO. > However, when we are doing IO that is almost all metadata (such as rm -rf'ing a > tree), then this patch speeds up the operation substantially. > > Incidentally, given that iscsi, sctp, and btrfs also use crc32c, this patchset > should improve their speed as well. I have not yet quantified that, however. I thought they usually used the SSE instruction for crc32 or equivalent. Joel -- "I almost ran over an angel He had a nice big fat cigar. 'In a sense,' he said, 'You're alone here So if you jump, you'd best jump far.'" http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
