From: Jeff King <peff@peff.net>
To: Duy Nguyen <pclouds@gmail.com>
Cc: "Derrick Stolee" <stolee@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"brian m. carlson" <sandals@crustytoothpaste.net>,
"Junio C Hamano" <gitster@pobox.com>,
"Git Mailing List" <git@vger.kernel.org>
Subject: Re: [ANNOUNCE] Git v2.19.0-rc0
Date: Wed, 22 Aug 2018 12:26:09 -0400 [thread overview]
Message-ID: <20180822162609.GA11904@sigill.intra.peff.net> (raw)
In-Reply-To: <CACsJy8DifmYtDE4D58yVM7rYhfJFe8p-t9bXgMmMsw=txxmzHA@mail.gmail.com>
On Wed, Aug 22, 2018 at 06:14:24PM +0200, Duy Nguyen wrote:
> On Wed, Aug 22, 2018 at 6:08 PM Duy Nguyen <pclouds@gmail.com> wrote:
> >
> > On Wed, Aug 22, 2018 at 6:03 PM Jeff King <peff@peff.net> wrote:
> > >
> > > On Wed, Aug 22, 2018 at 07:14:42AM -0400, Derrick Stolee wrote:
> > >
> > > > The other thing I was going to recommend (and I'll try to test this out
> > > > myself later) is to see if 'the_hash_algo->rawsz' is being treated as a
> > > > volatile variable, since it is being referenced through a pointer. Perhaps
> > > > storing the value locally and then casing on it would help?
> > >
> > > I tried various sprinkling of "const" around the declarations to make it
> > > clear that the values wouldn't change once we saw them. But I couldn't
> > > detect any difference. At most I think that would let us hoist the "if"
> > > out of the loop, but gcc still seems unwilling to expand the memcmp when
> > > there are other branches.
> > >
> > > I think if that's the thing we want to have happen, we really do need to
> > > just write it out on that branch rather than saying "memcmp".
> >
> > This reminds me of an old discussion about memcpy() vs doing explicit
> > compare loop with lots of performance measurements..
>
> Ah found it. Not sure if it is still relevant in light of multiple hash support
>
> https://public-inbox.org/git/20110427225114.GA16765@elte.hu/
Yes, that was what I meant. We actually did switch to that hand-rolled
loop, but later we went back to memcmp in 0b006014c8 (hashcmp: use
memcmp instead of open-coded loop, 2017-08-09).
-Peff
next prev parent reply other threads:[~2018-08-22 16:26 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-20 22:13 [ANNOUNCE] Git v2.19.0-rc0 Junio C Hamano
2018-08-20 22:41 ` Stefan Beller
2018-08-20 23:39 ` Jonathan Nieder
2018-08-21 0:27 ` Jonathan Nieder
2018-08-21 0:46 ` Stefan Beller
2018-08-21 20:41 ` Derrick Stolee
2018-08-21 21:29 ` Jeff King
2018-08-22 0:48 ` brian m. carlson
2018-08-22 3:03 ` Jeff King
2018-08-22 3:36 ` Jeff King
2018-08-22 11:11 ` Derrick Stolee
2018-08-22 5:36 ` brian m. carlson
2018-08-22 6:07 ` Jeff King
2018-08-22 7:39 ` Ævar Arnfjörð Bjarmason
2018-08-22 11:14 ` Derrick Stolee
2018-08-22 15:17 ` Jeff King
2018-08-22 16:08 ` Duy Nguyen
2018-08-22 16:14 ` Duy Nguyen
2018-08-22 16:26 ` Jeff King [this message]
2018-08-22 16:49 ` Derrick Stolee
2018-08-22 16:58 ` Duy Nguyen
2018-08-22 17:04 ` Derrick Stolee
2018-08-22 16:59 ` Jeff King
2018-08-22 17:02 ` Junio C Hamano
2018-08-22 15:14 ` Jeff King
2018-08-22 14:28 ` Derrick Stolee
2018-08-22 15:24 ` Jeff King
2018-08-22 12:42 ` Paul Smith
2018-08-22 15:23 ` Jeff King
2018-08-23 1:23 ` Jonathan Nieder
2018-08-23 2:16 ` Jeff King
2018-08-23 2:27 ` Jonathan Nieder
2018-08-23 5:02 ` Jeff King
2018-08-23 5:09 ` brian m. carlson
2018-08-23 5:10 ` Jonathan Nieder
2018-08-23 13:20 ` Junio C Hamano
2018-08-23 16:31 ` wide t/perf output, was " Jeff King
2018-08-23 3:47 ` brian m. carlson
2018-08-23 5:04 ` Jeff King
2018-08-23 10:26 ` Derrick Stolee
2018-08-23 13:16 ` Junio C Hamano
2018-08-23 16:14 ` Jeff King
2018-08-23 23:30 ` Jacob Keller
2018-08-23 23:40 ` Jeff King
2018-08-24 0:06 ` Jeff King
2018-08-24 0:16 ` Jeff King
2018-08-24 2:48 ` Jacob Keller
2018-08-24 2:59 ` Jeff King
2018-08-24 6:45 ` Jeff King
2018-08-24 11:04 ` Derrick Stolee
2018-08-27 19:36 ` Junio C Hamano
2018-08-23 18:53 ` Jeff King
2018-08-23 20:59 ` Derrick Stolee
2018-08-24 6:56 ` Jeff King
2018-08-24 7:57 ` Ævar Arnfjörð Bjarmason
2018-08-24 16:45 ` Derrick Stolee
2018-08-25 8:26 ` Jeff King
2018-09-02 18:53 ` Kaartic Sivaraam
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