I don't think we should go littering the Kconfig with defaults for various bits of hardware -- especially since you've already pointed out non-8xx hardware that would also want this. Put it in defconfig instead, unless you can identify very broad classes of machines for which SLICEBY4 is faster.
-Scott On Tue, 2013-11-19 at 15:11 +0100, Joakim Tjernlund wrote: > 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 > > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
