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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Jonathan Nieder <jrnieder@gmail.com>,
	Stefan Beller <sbeller@google.com>,
	Junio C Hamano <gitster@pobox.com>,
	Phillip Wood <phillip.wood@dunelm.org.uk>,
	"git@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: pushing for a new hash, was Re: [PATCH 2/3] rebase: Add tests for console output
Date: Thu, 15 Jun 2017 12:38:44 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1.1706151235480.4200@virtualbox> (raw)
In-Reply-To: <CACBZZX7JRA2niwt9wsGAxnzS+gWS8hTUgzWm8NaY1gs87o8xVQ@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 2941 bytes --]

Hi Ævar,

On Fri, 2 Jun 2017, Ævar Arnfjörð Bjarmason wrote:

> On Fri, Jun 2, 2017 at 7:54 PM, Jonathan Nieder <jrnieder@gmail.com> wrote:
> >
> > Johannes Schindelin wrote:
> >> On Thu, 1 Jun 2017, Stefan Beller wrote:
> >
> >>> We had a discussion off list how much of the test suite is in bad
> >>> shape, and "$ git grep ^index" points out a lot of places as well.
> >>
> >> Maybe we should call out a specific month (or even a longer period)
> >> during which we try to push toward that new hash function, and focus
> >> more on those tasks (and on critical bug fixes, if any) than anything
> >> else.
> >
> > Thanks for offering. ;-)
> >
> > Here's a rough list of some useful tasks, in no particular order:
> >
> > 1. bc/object-id: This patch series continues, eliminating assumptions
> >    about the size of object ids by encapsulating them in a struct.
> >    One straightforward way to find code that still needs to be
> >    converted is to grep for "sha" --- often the conversion patches
> >    change function and variable names to refer to oid_ where they used
> >    to use sha1_, making the stragglers easier to spot.
> >
> > 2. Hard-coded object ids in tests: As Stefan hinted, many tests beyond
> >    t00* make assumptions about the exact values of object ids.  That's
> >    bad for maintainability for other reasons beyond the hash function
> >    transition, too.
> >
> >    It should be possible to suss them out by patching git's sha1
> >    routine to use the ones-complement of sha1 (~sha1) instead and
> >    seeing which tests fail.
> 
> I just hacked this up locally.

Would you mind turning that into a patch? I figure this could be a
compile-time switch and applied to Git's `master` so that it is easier to
find those assumptions, as well as verify fixes on multiple platforms.

> > 4. When choosing a hash function, people may argue about performance.
> >    It would be useful for run some benchmarks for git (running
> >    the test suite, t/perf tests, etc) using a variety of hash
> >    functions as input to such a discussion.
> 
> To the extent that such benchmarks matter, it seems prudent to heavily
> weigh them in favor of whatever seems to be likely to be the more
> common hash function going forward, since those are likely to get
> faster through future hardware acceleration.

Exactly.

As I just mentioned elsewhere, the cryptographers I talked to expect
SHA-256 and SHA3-256 to see the most focus of all hash functions, by far.

> E.g. Intel announced Goldmont last year which according to one SHA-1
> implementation improved from 9.5 cycles per byte to 2.7 cpb[1]. They
> only have acceleration for SHA-1 and SHA-256[2]
> 
> 1. https://github.com/weidai11/cryptopp/issues/139#issuecomment-264283385
> 
> 2. https://en.wikipedia.org/wiki/Goldmont

Thanks for digging that up! Very valuable information.

Ciao,
Dscho

  reply	other threads:[~2017-06-15 10:38 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-31 10:42 [PATCH 0/3] Add regression tests for recent rebase -i fixes Phillip Wood
2017-05-31 10:42 ` [PATCH 1/3] rebase -i: Add test for reflog message Phillip Wood
2017-06-01  2:00   ` Junio C Hamano
2017-05-31 10:42 ` [PATCH 2/3] rebase: Add tests for console output Phillip Wood
2017-05-31 19:02   ` Phillip Wood
2017-06-01  1:59     ` Junio C Hamano
2017-06-01 12:56   ` Johannes Schindelin
2017-06-01 23:40     ` Junio C Hamano
2017-06-01 23:47       ` Stefan Beller
2017-06-02 12:47         ` pushing for a new hash, was " Johannes Schindelin
2017-06-02 17:54           ` Jonathan Nieder
2017-06-02 18:05             ` Jonathan Nieder
2017-06-02 20:29             ` Ævar Arnfjörð Bjarmason
2017-06-15 10:38               ` Johannes Schindelin [this message]
2017-06-03  0:36             ` Junio C Hamano
2017-06-06 22:22             ` Johannes Schindelin
2017-06-06 22:45               ` Jonathan Nieder
2017-06-07  1:09                 ` Junio C Hamano
2017-06-07  2:18                   ` [PATCH] t4005: modernize style and drop hard coded sha1 Stefan Beller
2017-06-07 17:39                     ` Brandon Williams
2017-06-06 22:45               ` pushing for a new hash, was Re: [PATCH 2/3] rebase: Add tests for console output Stefan Beller
2017-06-06 22:52                 ` Jonathan Nieder
2017-06-07  0:34                 ` Samuel Lijin
2017-06-07 14:47                 ` Johannes Schindelin
2017-06-07 16:53                   ` Stefan Beller
2017-06-07 10:47     ` Phillip Wood
2017-06-09 16:39       ` Junio C Hamano
2017-06-14 10:18         ` Phillip Wood
2017-06-14 12:51       ` Johannes Schindelin
2017-05-31 10:42 ` [PATCH 3/3] rebase: Add tests for console output with conflicting stash Phillip Wood
2017-06-14 10:24 ` [PATCH v2 0/3] Add regression tests for rectent rebase -i fixes Phillip Wood
2017-06-14 10:24   ` [PATCH v2 1/3] rebase -i: Add test for reflog message Phillip Wood
2017-06-14 10:24   ` [PATCH v2 2/3] rebase: Add regression tests for console output Phillip Wood
2017-06-14 10:24   ` [PATCH v2 3/3] rebase: Add more " Phillip Wood
2017-06-14 20:35   ` [PATCH v2 0/3] Add regression tests for rectent rebase -i fixes Johannes Schindelin
2017-06-15 23:05   ` Junio C Hamano
2017-06-15 23:23     ` Junio C Hamano
2017-06-15 23:29       ` Junio C Hamano
2017-06-16 13:49         ` Johannes Schindelin
2017-06-16 18:43           ` Johannes Sixt
2017-06-16 21:05             ` Junio C Hamano
2017-06-19 19:45             ` Johannes Sixt
2017-06-19 20:02               ` Junio C Hamano
2017-06-19  9:49           ` Phillip Wood
2017-06-19 15:45             ` Junio C Hamano
2017-06-19  9:52         ` Phillip Wood
2017-06-19 17:56 ` [PATCH v3 0/4] Add regression tests for recent " Phillip Wood
2017-06-19 17:56   ` [PATCH v3 1/4] sequencer: print autostash messages to stderr Phillip Wood
2017-06-19 17:56   ` [PATCH v3 2/4] rebase -i: Add test for reflog message Phillip Wood
2017-06-19 17:56   ` [PATCH v3 3/4] rebase: Add regression tests for console output Phillip Wood
2017-06-19 17:56   ` [PATCH v3 4/4] rebase: Add more " Phillip Wood
2017-06-23  4:17   ` [PATCH v3 0/4] Add regression tests for recent rebase -i fixes Junio C Hamano
2017-06-23  5:07     ` Junio C Hamano
2017-06-23  9:53       ` Phillip Wood
2017-06-23 17:03         ` Junio C Hamano
2017-06-23 18:53           ` Junio C Hamano
2017-06-26  9:17             ` Phillip Wood
2017-06-23 19:01           ` Junio C Hamano
2017-06-26  9:23             ` Phillip Wood

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