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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Stefan Beller" <sbeller@google.com>, git <git@vger.kernel.org>,
	"Junio C Hamano" <gitster@pobox.com>,
	"Thomas Rast" <tr@thomasrast.ch>,
	"Phil Haack" <haacked@gmail.com>, "Jason Frey" <jfrey@redhat.com>,
	"Philip Oakley" <philipoakley@iee.org>,
	"Duy Nguyen" <pclouds@gmail.com>
Subject: Re: A potential approach to making tests faster on Windows
Date: Tue, 3 Apr 2018 18:00:05 +0200 (DST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.1804031758160.5026@qfpub.tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20180403132717.GC18824@sigill.intra.peff.net>

Hi Peff,

On Tue, 3 Apr 2018, Jeff King wrote:

> On Tue, Apr 03, 2018 at 01:43:10PM +0200, Johannes Schindelin wrote:
> 
> > > I don't have time or interest to work on this now, but thought it was
> > > interesting to share. This assumes that something in shellscript like:
> > > 
> > >     while echo foo; do echo bar; done
> > > 
> > > Is no slower on Windows than *nix, since it's purely using built-ins, as
> > > opposed to something that would shell out.
> > 
> > It is still interpreting stuff. And it still goes through the POSIX
> > emulation layer.
> > 
> > I did see reports on the Git for Windows bug tracker that gave me the
> > impression that such loops in Unix shell scripts may not, in fact, be as
> > performant in MSYS2's Bash as you would like to believe:
> > 
> > https://github.com/git-for-windows/git/issues/1533#issuecomment-372025449
> 
> The main problem with `read` loops in shell is that the shell makes one
> read() syscall per character. It has to, because doing otherwise is
> user-visible in cases where the descriptor may get passed to a different
> process.

Thank you for the explanation. Makes tons of sense now.

> There's unfortunately no portable way to say "please just read this
> quickly, I promise nobody else is going to read the descriptor". And nor
> do I know of any shell which is smart enough to know that it's going to
> consume to EOF anyway (as you would for something like "cmd | while
> read").
> 
> If you know you have bash, you can use "-N" to get a more efficient
> read:
> 
>   $ echo foo | strace -e read bash -c 'read foo'
>   [...]
>   read(0, "f", 1)                         = 1
>   read(0, "o", 1)                         = 1
>   read(0, "o", 1)                         = 1
>   read(0, "\n", 1)                        = 1
> 
>   $ echo foo | strace -e read bash -c 'read -N 10 foo'
>   [...]
>   read(0, "foo\n", 10)                    = 4
>   read(0, "", 6)                          = 0
> 
> but then you have another problem: how to split the resulting buffer
> into lines in shell. ;)

True.

> But if we're at the point of creating custom C builtins for
> busybox/dash/etc, you should be able to create a primitive for "read
> this using buffered stdio, other processes be damned, and return one
> line at a time".

Well, you know, I do not think that papering over the root cause will make
anything better. And the root cause is that we use a test framework
written in Unix shell.

I will have to set aside some time to dig into the bottlenecks there and
figure out what parts I can safely convert into "test builtins", i.e. into
the test-tool Duy introduced, to avoid having shell scripts do the
heavy-lifting.

Ciao,
Dscho

  reply	other threads:[~2018-04-03 16:00 UTC|newest]

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-29 15:18 [PATCH 0/9] Assorted fixes for `git config` (including the "empty sections" bug) Johannes Schindelin
2018-03-29 15:18 ` [PATCH 1/9] git_config_set: fix off-by-two Johannes Schindelin
2018-03-29 18:15   ` Stefan Beller
2018-03-29 19:41     ` Jeff King
2018-03-30 12:32       ` Johannes Schindelin
2018-03-30 14:15         ` Ævar Arnfjörð Bjarmason
2018-03-30 16:24           ` Junio C Hamano
2018-03-30 18:44             ` Johannes Schindelin
2018-03-30 19:00               ` Junio C Hamano
2018-04-03  9:31                 ` Johannes Schindelin
2018-04-03 15:29                   ` Duy Nguyen
2018-04-03 15:47                     ` Johannes Schindelin
2018-04-08 23:12                   ` Junio C Hamano
2018-03-30 16:36         ` Duy Nguyen
2018-03-30 18:53           ` Johannes Schindelin
2018-03-30 19:16             ` Duy Nguyen
2018-03-30 18:45         ` A potential approach to making tests faster on Windows Ævar Arnfjörð Bjarmason
2018-03-30 18:58           ` Junio C Hamano
2018-03-30 19:16           ` Jeff King
2018-04-03  9:49             ` Johannes Schindelin
2018-04-03 11:28               ` Ævar Arnfjörð Bjarmason
2018-04-03 15:55                 ` Johannes Schindelin
2018-04-03 21:36               ` Eric Sunshine
2018-04-03 11:43           ` Johannes Schindelin
2018-04-03 13:27             ` Jeff King
2018-04-03 16:00               ` Johannes Schindelin [this message]
2018-04-06 21:40                 ` Jeff King
2018-04-06 21:57                   ` Stefan Beller
2018-03-29 15:18 ` [PATCH 2/9] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-03-29 19:42   ` Jeff King
2018-03-30 12:37     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 3/9] t1300: avoid relying on a bug Johannes Schindelin
2018-03-29 19:43   ` Jeff King
2018-03-30 12:38     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 4/9] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-03-29 19:52   ` Jeff King
2018-03-29 20:45     ` Junio C Hamano
2018-03-30 12:42     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 5/9] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-03-29 19:54   ` Jeff King
2018-03-29 15:18 ` [PATCH 6/9] git_config_set: simplify the way the section name is remembered Johannes Schindelin
2018-03-29 15:19 ` [PATCH 7/9] git config --unset: remove empty sections (in normal situations) Johannes Schindelin
2018-03-29 21:32   ` Jeff King
2018-03-30 13:00     ` Johannes Schindelin
2018-03-30 13:09       ` Jeff King
2018-03-29 15:19 ` [PATCH 8/9] git_config_set: use do_config_from_file() directly Johannes Schindelin
2018-03-29 21:38   ` Jeff King
2018-03-30 13:02     ` Johannes Schindelin
2018-03-30 13:14       ` Jeff King
2018-03-30 14:01         ` Johannes Schindelin
2018-03-30 14:08           ` Jeff King
2018-03-30 19:04             ` Johannes Schindelin
2018-03-29 15:19 ` [PATCH 9/9] git_config_set: reuse empty sections Johannes Schindelin
2018-03-29 21:50   ` Jeff King
2018-03-30 13:15     ` Johannes Schindelin
2018-03-29 17:58 ` [PATCH 0/9] Assorted fixes for `git config` (including the "empty sections" bug) Stefan Beller
2018-03-30 12:14   ` Johannes Schindelin
2018-03-29 19:39 ` Jeff King
2018-03-30 12:35   ` Johannes Schindelin
2018-03-30 14:17 ` Ævar Arnfjörð Bjarmason
2018-03-30 18:46   ` Johannes Schindelin
2018-04-03 16:27 ` [PATCH v2 00/15] " Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 01/15] git_config_set: fix off-by-two Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 02/15] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 03/15] t1300: demonstrate that --replace-all can "invent" newlines Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 04/15] config --replace-all: avoid extra line breaks Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 05/15] t1300: avoid relying on a bug Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 06/15] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 07/15] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 08/15] config: introduce an optional event stream while parsing Johannes Schindelin
2018-04-06 21:22     ` Jeff King
2018-04-09  7:35       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 09/15] config: avoid using the global variable `store` Johannes Schindelin
2018-04-06 21:23     ` Jeff King
2018-04-09  7:36       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 10/15] config_set_store: rename some fields for consistency Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 11/15] git_config_set: do not use a state machine Johannes Schindelin
2018-04-06 21:28     ` Jeff King
2018-04-09  7:50       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 12/15] git_config_set: make use of the config parser's event stream Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 13/15] git config --unset: remove empty sections (in the common case) Johannes Schindelin
2018-04-03 16:29   ` [PATCH v2 14/15] git_config_set: reuse empty sections Johannes Schindelin
2018-04-03 16:30   ` [PATCH v2 00/15] Assorted fixes for `git config` (including the "empty sections" bug) Johannes Schindelin
2018-04-06 21:33   ` Jeff King
2018-04-09  8:19     ` Johannes Schindelin
2018-04-09  8:31   ` [PATCH v3 " Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 01/15] git_config_set: fix off-by-two Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 02/15] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 03/15] t1300: demonstrate that --replace-all can "invent" newlines Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 04/15] config --replace-all: avoid extra line breaks Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 05/15] t1300: avoid relying on a bug Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 06/15] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 07/15] t1300: add a few more hairy examples of sections becoming empty Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 08/15] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 09/15] config: introduce an optional event stream while parsing Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 10/15] config: avoid using the global variable `store` Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 11/15] config_set_store: rename some fields for consistency Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 12/15] git_config_set: do not use a state machine Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 13/15] git_config_set: make use of the config parser's event stream Johannes Schindelin
2018-05-08 13:42       ` Jeff King
2018-05-08 14:00         ` Jeff King
2018-04-09  8:32     ` [PATCH v3 14/15] git config --unset: remove empty sections (in the common case) Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 15/15] git_config_set: reuse empty sections Johannes Schindelin

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