From: "Bob Pearson" <rpearson@systemfabricworks.com>
To: "'Joakim Tjernlund'" <joakim.tjernlund@transmode.se>
Cc: "'Andrew Morton'" <akpm@linux-foundation.org>,
"'frank zago'" <fzago@systemfabricworks.com>,
<linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] add slice by 8 algorithm to crc32.c
Date: Fri, 5 Aug 2011 10:51:00 -0500 [thread overview]
Message-ID: <023b01cc5387$79b09dd0$6d11d970$@systemfabricworks.com> (raw)
In-Reply-To: <OF14136E0E.3F2388EF-ONC12578E3.00301969-C12578E3.00338524@transmode.se>
> > version. While I haven't done the experiment you suggest there is
> something
> > to the point that the second q computation in the new version can be
> moved
> > ahead of the table lookups from the first q computation . My guess is
that
> > the unrolled version will be significantly slower.
>
> Ah, didn't see that. Don't understand how this works though.
> Why do you do two 32 bit loads instead of one 64 bit load?
>
> >
The two expression trees can be computed in parallel and combined with the
final xor. If the compiler/instruction scheduler are smart enough and can
process enough instructions per cycle they overlap well and you get some
speedup. I did try a 64 bit load on Nehalem but got about 2 cycles per byte
which is a little worse than doing two loads and better than the 32 bit
version. I'm not really sure why.
next prev parent reply other threads:[~2011-08-05 15:51 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <OF4AE0115F.3AA5397E-ONC12578DF.002EC6DF-C12578DF.003348E5@transmode.se>
2011-08-02 21:14 ` [PATCH] add slice by 8 algorithm to crc32.c Bob Pearson
2011-08-02 21:19 ` Bob Pearson
2011-08-04 11:54 ` Joakim Tjernlund
2011-08-04 18:53 ` Bob Pearson
2011-08-05 9:22 ` Joakim Tjernlund
2011-08-05 15:51 ` Bob Pearson [this message]
2011-08-08 7:11 ` Joakim Tjernlund
2011-08-05 17:27 ` Bob Pearson
2011-08-08 7:15 ` Joakim Tjernlund
[not found] ` <OF14136E0E.3F2388EF-ONC12578E3.00301969-C12578E3.00338524@LocalDomain>
2011-08-05 13:34 ` Joakim Tjernlund
2011-08-08 9:28 George Spelvin
2011-08-08 10:31 ` Joakim Tjernlund
2011-08-08 10:52 ` George Spelvin
2011-08-08 11:11 ` Joakim Tjernlund
2011-08-08 17:04 ` Bob Pearson
[not found] ` <OFEA1BD2B2.B2A7F07F-ONC12578E6.003D368C-C12578E6.003D7468@LocalDomain>
2011-08-08 11:24 ` Joakim Tjernlund
2011-08-08 11:42 ` Joakim Tjernlund
2011-08-08 12:54 ` George Spelvin
2011-08-08 17:01 ` Bob Pearson
2011-08-08 20:45 ` George Spelvin
2011-08-08 22:21 ` Bob Pearson
2011-08-08 16:54 ` Bob Pearson
2011-08-08 16:50 ` Bob Pearson
-- strict thread matches above, loose matches on Subject: below --
2011-07-20 22:19 frank zago
2011-07-28 22:16 ` Andrew Morton
2011-07-29 1:47 ` Bob Pearson
2011-08-01 19:39 ` Andrew Morton
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