"Darrick J. Wong" <djwong@xxxxxxxxxx> wrote on 2011/09/30 21:29:56: > > The existing CRC32c implementation uses Sarwate's algorithm to calculate the > code one byte at a time. Using a slicing-by-8 algorithm adapted from Bob > Pearson, we can process buffers 8 bytes at a time, for a substantial increase > in performance. > > The motivation for this patchset is that I am working on adding full metadata > checksumming to ext4 and jbd2. 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 metadata operations (file creation > and deletion, and fallocate/truncate), 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. > > Given that iscsi, sctp, and btrfs also use crc32c, this patchset should improve > their speed as well. I have some preliminary results[1] that show the > difference in various crc algorithms that I've come across: the "crc32c-by8-le" > column is the new algorithm in the patch; the "crc32c" column is the current > crc32c kernel implementation; and the "crc32-kern-le" column is the current > crc32 kernel implementation, which is similar to the results one gets for > CONFIG_CRC32C_SLICEBY4=y. As you can see, the new implementation runs at > nearly 4x the speed of the current implementation; even the slimmer slice-by-4 > implementation is generally 2-3x faster. > > However, the implementation allows the kernel builder to select from a variety > of space-speed tradeoffs, should my results not hold true on a particular > class of system. > > v2: Use the crypto testmgr api for self-test. > v3: Get rid of the -be version, which had no users. > v4: Allow kernel builder a choice of speed vs. space optimization. > > [1]http://djwong.org/docs/ext4_metadata_checksums.html > (cached copy of the ext4 wiki) > > Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> This is based on an old version of Bobs slice by 8 that has lots duplication and hard to maintain. Start from Bobs latest patches and add crc32c to lib/crc32.c Also, for crc32c I think you only need slice by 4 and slice by 8 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
