From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>,
"brian m. carlson" <sandals@crustytoothpaste.net>,
Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org
Subject: Re: [ANNOUNCE] Git v2.19.0-rc0
Date: Wed, 22 Aug 2018 07:11:54 -0400 [thread overview]
Message-ID: <b60e8d18-261c-c86d-b5e0-b06a5d46d9ea@gmail.com> (raw)
In-Reply-To: <20180822033654.GA30196@sigill.intra.peff.net>
On 8/21/2018 11:36 PM, Jeff King wrote:
> On Tue, Aug 21, 2018 at 11:03:44PM -0400, Jeff King wrote:
>
>> with the obvious "oideq()" implementation added, that seems to get me to
>> 2-3%. Not _quite_ as good as the original branching version I showed.
>> And we had to touch all the callsites (although arguably that kind of
>> "eq" function is a better interface anyway, since it obviously allows
>> for more optimization.
>>
>> So maybe the branching thing is actually not so insane. It makes new
>> hash_algo's Just Work; they just won't be optimized. And the change is
>> very localized.
> Hmph. So I went back to double-check my measurements on that branching
> version, and I couldn't replicate it!
I'm actually relieved to see this, as I couldn't either.
>
> It turns out what I showed (and measured) before has a bug. Can you see
> it?
I had rewritten the section from scratch instead of applying your diff,
so I didn't get the sha1-sha1 error. I decided to sleep on it instead of
sending my email.
> So the assert() version really is the fastest. I didn't test, but I
> suspect we could "trick" the compiler by having the fallback call an
> opaque wrapper around memcmp(). That would prevent it from combining the
> two paths, and presumably it would still optimize the constant-20 side.
> Or maybe it would eventually decide our inline function is getting too
> big and scrap it. Which probably crosses a line of craziness (if I
> didn't already cross it two emails ago).
I appreciate your effort here.
Thanks
-Stolee
next prev parent reply other threads:[~2018-08-22 11:12 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 [this message]
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
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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