On Wed, 18 Jan 2012 14:27:33 -0800 "Darrick J. Wong" <djwong@xxxxxxxxxx> wrote: > 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. > This latest submission combines Bob's patches from late August 2011 with mine > so that they can be one coherent patch set. Please excuse my inability to > combine some of the patches; I've been advised to leave Bob's patches alone and > build atop them instead. :/ > > Since the last posting, I've also collected some crc32c test results on a bunch > of different x86/powerpc/sparc platforms. The results can be viewed here: > http://goo.gl/sgt3i ; the "crc32-kern-le" and "crc32c" columns describe the > performance of the kernel's current crc32 and crc32c software implementations. > The "crc32c-by8-le" column shows crc32c performance with this patchset applied. > I expect crc32 performance to be roughly the same. > > The two _boost columns at the right side of the spreadsheet shows how much > faster the new implementation is over the old one. As you can see, crc32 rises > substantially, and crc32c experiences a huge increase. I grabbed this lot, so it will turn up in linux-next soon. There are quite a lot of clients of the crc32 code. net, netfilter and wireless are prominent, but there are others everywhere. So I cc'ed various other mailing lists just as a heads-up that this work is inbound and will hopefully yield performance improvements. But of course, it might also yield bugs. -- 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
