From: "H. Peter Anvin" <hpa@zytor•com>
To: Alex Riesen <raa.lkml@gmail•com>
Cc: kusmabite@gmail•com, "Pekka Enberg" <penberg@cs•helsinki.fi>,
"Ingo Molnar" <mingo@elte•hu>,
"Junio C Hamano" <gitster@pobox•com>,
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>
Subject: Re: [PATCH] git gc: Speed it up by 18% via faster hash comparisons
Date: Fri, 29 Apr 2011 09:24:08 -0700 [thread overview]
Message-ID: <4DBAE628.4080501@zytor.com> (raw)
In-Reply-To: <BANLkTikt0CU87maPs65WGi0oopD+g0uVDA@mail.gmail.com>
On 04/29/2011 12:05 AM, Alex Riesen wrote:
>
> Can one take advantage of common expression optimization here?
> Like this:
>
> + if (*sha1 - *sha2)
> + return *sha1 - *sha2;
>
Or even clue the compiler in explicitly:
delta = *sha1 - *sha2;
if (delta)
return delta;
For newer x86-specific optimization there are a bunch of newer SSE
instructions which can be used to do bulk compares which may be faster
if optimized for the fixed length compare; of course it requires a new
enough processor.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2011-04-29 16:27 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
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 [this message]
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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