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    SubjectRe: [PATCH v5.2 00/14] crc32c: Add faster algorithm and self-test code
    On Thu, Dec 01, 2011 at 12:13:41PM -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.

    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.'"

    http://www.jlbec.org/
    jlbec@evilplan.org


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