[PATCH v5 0/4] crc32c: Add faster algorithm and self-test code

From: Darrick J. Wong
Date: Tue Oct 04 2011 - 19:54:19 EST

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.

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