From: "H. Peter Anvin" <hpa@zytor.com>
To: kusmabite@gmail.com
Cc: "Andreas Ericsson" <ae@op5.se>,
"Bernhard R. Link"
<brl+ccmadness@pcpool00.mathematik.uni-freiburg.de>,
"Ralf Baechle" <ralf@linux-mips.org>,
"Junio C Hamano" <gitster@pobox.com>,
"Ingo Molnar" <mingo@elte.hu>,
git@vger.kernel.org, "Thomas Gleixner" <tglx@linutronix.de>,
"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
"Arnaldo Carvalho de Melo" <acme@redhat.com>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Pekka Enberg" <penberg@cs.helsinki.fi>
Subject: Re: [PATCH] git gc: Speed it up by 18% via faster hash comparisons
Date: Thu, 28 Apr 2011 13:19:04 -0700 [thread overview]
Message-ID: <4DB9CBB8.8050605@zytor.com> (raw)
In-Reply-To: <BANLkTikU3evfo86WmQeVS_Z41s3xSK1DJw@mail.gmail.com>
On 04/28/2011 02:55 AM, Erik Faye-Lund wrote:
>
> I disagree. We have no guarantee that the SHA-1s are aligned on x86
> either, and unaligned accesses are slow on x86.
>
Not particularly, especially not statistically. Furthermore, for a
sizable chunk like a SHA-1, not all accesses will have the cross-grain
penalities that you sometimes can have.
> I think it's much much cleaner to add an early-out on the first byte,
> and hope that memcmp is optimized properly. If it's not, those
> platforms can add an override to memcmp in git-compat-util and/or
> compat/*.
Overall, doing an architecture optimization library especially for
widely used architectures like x86 is not a bad idea.
-hpa
next prev parent reply other threads:[~2011-04-28 20:22 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-27 22:51 [PATCH] git gc: Speed it up by 18% via faster hash comparisons Ingo Molnar
2011-04-27 23:10 ` Ingo Molnar
2011-04-27 23:18 ` Jonathan Nieder
2011-04-28 6:36 ` Ingo Molnar
2011-04-28 9:31 ` Jonathan Nieder
2011-04-28 10:36 ` Ingo Molnar
2011-04-28 9:32 ` Dmitry Potapov
2011-04-27 23:32 ` Junio C Hamano
2011-04-28 0:35 ` Ralf Baechle
2011-04-28 8:18 ` Bernhard R. Link
2011-04-28 9:42 ` Andreas Ericsson
2011-04-28 9:55 ` Erik Faye-Lund
2011-04-28 20:19 ` H. Peter Anvin [this message]
2011-04-28 6:27 ` Ingo Molnar
2011-04-28 9:17 ` Erik Faye-Lund
2011-04-28 9:33 ` Ingo Molnar
2011-04-28 9:37 ` Ingo Molnar
2011-04-28 9:50 ` Erik Faye-Lund
2011-04-28 10:10 ` Pekka Enberg
2011-04-28 10:19 ` Erik Faye-Lund
2011-04-28 10:30 ` Pekka Enberg
2011-04-28 11:59 ` Erik Faye-Lund
2011-04-28 12:12 ` Pekka Enberg
2011-04-28 12:36 ` Jonathan Nieder
2011-04-28 12:40 ` Erik Faye-Lund
2011-04-28 13:37 ` Ingo Molnar
2011-04-28 15:14 ` Ingo Molnar
2011-04-28 16:00 ` Erik Faye-Lund
2011-04-28 20:32 ` Ingo Molnar
2011-04-29 7:05 ` Alex Riesen
2011-04-29 16:24 ` H. Peter Anvin
2011-04-28 12:16 ` Tor Arntsen
2011-04-28 20:23 ` H. Peter Anvin
2011-04-28 12:17 ` Andreas Ericsson
2011-04-28 12:28 ` Erik Faye-Lund
2011-04-28 10:19 ` Ingo Molnar
2011-04-28 12:02 ` Nguyen Thai Ngoc Duy
2011-04-28 12:18 ` Erik Faye-Lund
2011-04-28 20:20 ` Junio C Hamano
2011-04-28 16:36 ` Dmitry Potapov
2011-04-28 8:52 ` Dmitry Potapov
2011-04-28 9:11 ` Ingo Molnar
2011-04-28 9:31 ` Dmitry Potapov
2011-04-28 9:44 ` Ingo Molnar
2011-04-28 9:38 ` Ingo Molnar
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