On Tue, Sep 27, 2011 at 03:12:39PM -0700, Darrick J. Wong wrote:

Hi all,

This patchset replaces the current crc32c software implementation, which uses a
slow per-byte lookup table algorithm, with a faster implementation that uses an
adaptation of the slice-by-8 algorithm that Bob Pearson has been pushing for
crc32.

The motivation for this patchset is that I am working on adding full metadata
checksumming to ext4[1].  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.

Please have a look at the patches, and please feel free to suggest any changes.
I will be at LPC next week if anyone wishes to discuss, debate, or protest.

Oops, ignore that sentence, since LPC has long passed. :(

--D

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.

v2: Use the crypto test manager code to check crc32c operation.

--D

[1] https://ext4.wiki.kernel.org/index.php/Ext4_Metadata_Checksums