"Darrick J. Wong" <djwong@xxxxxxxxxx> wrote on 2011/10/06 22:20:42: > Subject: Re: [PATCH v5 0/4] crc32c: Add faster algorithm and self-test code > > On Tue, Oct 04, 2011 at 04:53:57PM -0700, 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 requires that all ten of his patches (at > > least the ones dated 31 Aug 2011) be applied. 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. > > As for Mr. Tjernlund's unresolved questions regarding the v4 patch, I have > tested this new code on x64/x32/ppc32/ppc64 and it seems to work fine, both > with the crc32c selftest and also on a practical level with ext4 metadata > checksumming enabled. Updating to Bob's newest calculation code brings about a > 10-15% speedup on the ppc64 box. I also see that slice-by-8 is about 20% > faster than slice-by-4 on my ppc32 box. > > I did _not_ see any failures on ppc32 when running an extended ext4+checksum > test suite. Hi Darrick, I finally had some time to look this series over and I like this much better. Thank you for your patience with me :) Acked-By: Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx> Jocke -- 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
