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    SubjectRe: [PATCH v5.2 00/14] crc32c: Add faster algorithm and self-test code
    On Thu, Dec 01, 2011 at 12:20:53PM -0800, Joel Becker wrote:
    > On Thu, Dec 01, 2011 at 12:13:41PM -0800, 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 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.
    > I thought they usually used the SSE instruction for crc32 or
    > equivalent.

    They seem to call crc32c(), which is in crypto/crc32c. If you're interested in
    hardware accelerated crc32c on Intel, it is still the case that the wrapper for
    that can be loaded via crc32c-intel.

    > Joel
    > --
    > "I almost ran over an angel
    > He had a nice big fat cigar.
    > 'In a sense,' he said, 'You're alone here
    > So if you jump, you'd best jump far.'"

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