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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='023b01cc5387$79b09dd0$6d11d970$@systemfabricworks.com' \
--to=rpearson@systemfabricworks.com \
--cc=akpm@linux-foundation.org \
--cc=fzago@systemfabricworks.com \
--cc=joakim.tjernlund@transmode.se \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.