I found the same on MPC8321 long time ago(when 64 bits change went in), the 32 bits were much faster. I guess the "smaller" CPUs cannot handle the cache trashing these big tables impose, I didn't look into the details though. So I think this is a good change for 8xx.
Acked-by: Joakim Tjernlund <joakim.tjernl...@transmode.se> Christophe Leroy <christophe.le...@c-s.fr> wrote on 2013/11/18 08:04:23: > From: Christophe Leroy <christophe.le...@c-s.fr> > To: Vitaly Bordug <v...@kernel.crashing.org>, Marcelo Tosatti <marc...@kvack.org>, Joakim Tjernlund <joakim.tjernl...@transmode.se>, Bob Pearson <rpear...@systemfabricworks.com>, > Cc: linux-ker...@vger.kernel.org, linuxppc-dev@lists.ozlabs.org > Date: 2013/11/19 13:05 > Subject: [PATCH] lib/crc32: slice by 4 is more efficient than the default slice by 8 on Powerpc 8xx. > > On PPC_8xx, CRC32_SLICEBY4 is more efficient (almost twice) than CRC32_SLICEBY8, > as shown below: > > With CRC32_SLICEBY8: > [ 1.109204] crc32: CRC_LE_BITS = 64, CRC_BE BITS = 64 > [ 1.114401] crc32: self tests passed, processed 225944 bytes in 15118910 nsec > [ 1.130655] crc32c: CRC_LE_BITS = 64 > [ 1.134235] crc32c: self tests passed, processed 225944 bytes in 4479879 nsec > > With CRC32_SLICEBY4: > [ 1.097129] crc32: CRC_LE_BITS = 32, CRC_BE BITS = 32 > [ 1.101878] crc32: self tests passed, processed 225944 bytes in 8616242 nsec > [ 1.116298] crc32c: CRC_LE_BITS = 32 > [ 1.119607] crc32c: self tests passed, processed 225944 bytes in 3289576 nsec > > Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr> > > Index: a/lib/Kconfig > =================================================================== > --- a/lib/Kconfig (révision 5325) > +++ b/lib/Kconfig (copie de travail) > @@ -102,6 +102,7 @@ > choice > prompt "CRC32 implementation" > depends on CRC32 > + default CRC32_SLICEBY4 if PPC_8xx > default CRC32_SLICEBY8 > help > This option allows a kernel builder to override the default choice _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
