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    SubjectRE: [patch v3 7/7] crc32: final-cleanup.diff
    Date


    > -----Original Message-----
    > From: Joakim Tjernlund [mailto:joakim.tjernlund@transmode.se]
    > Sent: Wednesday, August 10, 2011 10:49 AM
    > To: Bob Pearson
    > Cc: akpm@linux-foundation.org; fzago@systemfabricworks.com; 'George
    > Spelvin'; linux-kernel@vger.kernel.org
    > Subject: RE: [patch v3 7/7] crc32: final-cleanup.diff
    >
    > "Bob Pearson" <rpearson@systemfabricworks.com> wrote on 2011/08/10
    > 17:13:00:
    >
    > > From: "Bob Pearson" <rpearson@systemfabricworks.com>
    > > To: "'Joakim Tjernlund'" <joakim.tjernlund@transmode.se>
    > > Cc: <akpm@linux-foundation.org>, <fzago@systemfabricworks.com>,
    > "'George Spelvin'" <linux@horizon.com>, <linux-kernel@vger.kernel.org>
    > > Date: 2011/08/10 17:13
    > > Subject: RE: [patch v3 7/7] crc32: final-cleanup.diff
    > >
    > > OK. Can you post your current version of crc32.c? I'll try to merge them
    > > together.
    >
    > OK, here it comes again, prefably this should be the first patch
    > in the series.
    >
    > From f5268d74f1a81610820e92785397f1247946ce15 Mon Sep 17 00:00:00 2001
    > From: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
    > Date: Fri, 5 Aug 2011 17:49:42 +0200
    > Subject: [PATCH] crc32: Optimize inner loop.
    >
    > taking a pointer reference to each row in the crc table matrix,
    > one can reduce the inner loop with a few insn's on RISC
    > archs like PowerPC.
    > ---
    > lib/crc32.c | 21 +++++++++++----------
    > 1 files changed, 11 insertions(+), 10 deletions(-)
    >
    > diff --git a/lib/crc32.c b/lib/crc32.c
    > index 4855995..b06d1e7 100644
    > --- a/lib/crc32.c
    > +++ b/lib/crc32.c
    > @@ -51,20 +51,21 @@ static inline u32
    > crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32
    > (*tab)[256])
    > {
    > # ifdef __LITTLE_ENDIAN
    > -# define DO_CRC(x) crc = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)
    > -# define DO_CRC4 crc = tab[3][(crc) & 255] ^ \
    > - tab[2][(crc >> 8) & 255] ^ \
    > - tab[1][(crc >> 16) & 255] ^ \
    > - tab[0][(crc >> 24) & 255]
    > +# define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
    > +# define DO_CRC4 crc = t3[(crc) & 255] ^ \
    > + t2[(crc >> 8) & 255] ^ \
    > + t1[(crc >> 16) & 255] ^ \
    > + t0[(crc >> 24) & 255]
    > # else
    > -# define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
    > -# define DO_CRC4 crc = tab[0][(crc) & 255] ^ \
    > - tab[1][(crc >> 8) & 255] ^ \
    > - tab[2][(crc >> 16) & 255] ^ \
    > - tab[3][(crc >> 24) & 255]
    > +# define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
    > +# define DO_CRC4 crc = t0[(crc) & 255] ^ \
    > + t1[(crc >> 8) & 255] ^ \
    > + t2[(crc >> 16) & 255] ^ \
    > + t3[(crc >> 24) & 255]
    > # endif
    > const u32 *b;
    > size_t rem_len;
    > + const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];
    >
    > /* Align it */
    > if (unlikely((long)buf & 3 && len)) {
    > --
    > 1.7.3.4

    I tried this on X86_64 and Sparc 64. Very small improvement for Intel and
    significant improvement for Sparc. Here are the results based on current
    self test which is a mix of crc32_le and crc32_be with random offsets and
    lengths:
    Results are 'best case' I.e. I picked the shortest time from a handful of
    runs.

    Arch CPU Freq BITS bytes
    nsec cycles/byte

    ____________________________________________________________________________
    Current proposed patch
    X86_64 Intel E5520 2.268G 64 225944
    161294 1.619
    X86_64 Intel E5520 2.268G 32 225944
    267795 2.688
    Sun Sparc III+ 900M 64 225944
    757235 3.028
    Sun Sparc III+ 900M 32 225944
    935558 3.727
    With pointers instead of 2D array references
    X86_64 E5520 2.268G 64 225944
    157975 1.584
    X86_64 E5520 2.268M 32 225944
    273366 2.744
    Sun Sparc III+ 900M 64 225944
    570724 2.273
    Sun Sparc III+ 900M 32 225944
    848897 3.381

    The change doesn't really help or hurt for X86_64 but significantly helps
    Sparc and you report gains for PPC so it looks good.



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