• Bob Pearson's avatar
    crc32: remove two instances of trailing whitespaces · e30c7a8f
    Bob Pearson authored
    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.
    This patch:
    - remove trailing whitespace from lib/crc32.c
    - remove trailing whitespace from lib/crc32defs.h
    [djwong@us.ibm.com: changelog tweaks]
    Signed-off-by: default avatarBob Pearson <rpearson@systemfabricworks.com>
    Signed-off-by: default avatarDarrick J. Wong <djwong@us.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
crc32.c 14.5 KB