From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
"Glen Choo" <chooglen@google.com>,
"Jonas Bernoulli" <jonas@bernoul.li>, "Jeff King" <peff@peff.net>,
"Emily Shaffer" <emilyshaffer@google.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: [PATCH 10/10] submodule: don't use a subprocess to invoke "submodule--helper"
Date: Mon, 17 Oct 2022 14:09:25 +0200 [thread overview]
Message-ID: <patch-10.10-81f138e460c-20221017T115544Z-avarab@gmail.com> (raw)
In-Reply-To: <cover-00.10-00000000000-20221017T115544Z-avarab@gmail.com>
In a preceding commit we created "builtin/submodule.c" and faithfully
tried to reproduce every aspect of "git-submodule.sh", including its
invocation of "git submodule--helper" as a sub-process.
Let's do away with the sub-process and invoke
"cmd_submodule__helper()" directly. Eventually we'll want to do away
with "builtin/submodule--helper.c" altogether, but let's not do that
for now to avoid conflicts with other in-flight topics. Even without
those conflicts the resulting diff would be large. We can leave that
for a later cleanup.
This speeds up invocations of all "git submodule" commands, E.g. a
trivial "foreach" command on git.git is around 1.50 times
faster[1]. For more expensive commands this'll make less of a
difference, as the fixed cost of invoking the sub-process will be
amortized away.
$ git hyperfine -L rev HEAD~1,HEAD -s 'make CFLAGS=-O3' './git submodule foreach "echo \$name"'
Benchmark 1: ./git submodule foreach "echo \$name"' in 'HEAD~1
Time (mean ± σ): 9.7 ms ± 0.1 ms [User: 7.6 ms, System: 2.1 ms]
Range (min … max): 9.4 ms … 10.2 ms 285 runs
Benchmark 2: ./git submodule foreach "echo \$name"' in 'HEAD
Time (mean ± σ): 6.6 ms ± 0.1 ms [User: 5.1 ms, System: 1.5 ms]
Range (min … max): 6.2 ms … 7.2 ms 414 runs
Summary
'./git submodule foreach "echo \$name"' in 'HEAD' ran
1.48 ± 0.04 times faster than './git submodule foreach "echo \$name"' in 'HEAD~1'
It's also worth noting that some users were using e.g. "git
submodule--helper list" directly for performance reasons[2]. With
31955475d1c (submodule--helper: remove unused "list" helper,
2022-09-01) released with v2.38.0 the "list" command was no longer
provided. Users who had to switch to "git submodule--helper foreach"
were given a command that (on my system) is around 6.5x slower.
Now the "foreach" is around 0.10x slower (due to the slight shell
overhead), with 31955475d1c reverted on top of this:
$ hyperfine './git submodule--helper list' './git submodule foreach --quiet "echo \$name"' --warmup 10
Benchmark 1: ./git submodule--helper list
Time (mean ± σ): 6.4 ms ± 0.1 ms [User: 5.0 ms, System: 1.5 ms]
Range (min … max): 6.2 ms … 7.2 ms 427 runs
Benchmark 2: ./git submodule foreach --quiet "echo \$name"
Time (mean ± σ): 7.0 ms ± 0.1 ms [User: 4.8 ms, System: 2.3 ms]
Range (min … max): 6.8 ms … 7.4 ms 390 runs
Summary
'./git submodule--helper list' ran
1.10 ± 0.03 times faster than './git submodule foreach --quiet "echo \$name"'
I think it would make sense to implement a "--format" option for "git
submodule foreach" to help anyone who cares about that remaining
performance (and to improve the API, e.g. by supporting "-z"), but as
far as performance goes this makes the runtime acceptable again.
The pattern in "cmd_submodule_builtin()" of saving "struct strvec"
arguments to a "struct string_list" and free()-ing them after the
"argv" has been modified by "cmd_submodule__helper()" is new, without
it we'd get various already-passing tests failing under SANITIZE=leak.
1. Using the "git hyperfine" wrapper for "hyperfine":
https://lore.kernel.org/git/211201.86r1aw9gbd.gmgdl@evledraar.gmail.com/
2. https://lore.kernel.org/git/87czatrpyb.fsf@bernoul.li/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
builtin/submodule.c | 41 +++++++++++++++++++++++++++++++++--------
1 file changed, 33 insertions(+), 8 deletions(-)
diff --git a/builtin/submodule.c b/builtin/submodule.c
index ca8e273b6e9..13e7064b03f 100644
--- a/builtin/submodule.c
+++ b/builtin/submodule.c
@@ -119,12 +119,40 @@ static void setup_helper_args(int argc, const char **argv, const char *prefix,
strvec_pushv(args, argv);
}
+static int cmd_submodule_builtin(struct strvec *args, const char *prefix)
+{
+ size_t i;
+ struct string_list to_free = STRING_LIST_INIT_DUP;
+ int ret;
+
+ /*
+ * The cmd_submodule__helper() will treat the argv as
+ * its own and modify it, so e.g. for "git submodule
+ * add" the "add" argument will be removed, and we'll
+ * thus leak from the strvec_push()'s in
+ * setup_helper_args().
+ *
+ * So in lieu of some generic "snapshot for a free"
+ * API for "struct strvec" squirrel away the pointers
+ * to free with string_list_clear() later.
+ */
+ for (i = 0; i < args->nr; i++)
+ string_list_append_nodup(&to_free, (char *)args->v[i]);
+
+ ret = cmd_submodule__helper(args->nr, args->v, prefix);
+
+ string_list_clear(&to_free, 0);
+ free(strvec_detach(args));
+
+ return ret;
+}
+
int cmd_submodule(int argc, const char **argv, const char *prefix)
{
int opt_quiet = 0;
int opt_cached = 0;
int opt_recursive = 0;
- struct child_process cp = CHILD_PROCESS_INIT;
+ struct strvec args = STRVEC_INIT;
struct option options[] = {
OPT__QUIET(&opt_quiet, N_("be quiet")),
OPT_BOOL(0, "cached", &opt_cached,
@@ -141,13 +169,10 @@ int cmd_submodule(int argc, const char **argv, const char *prefix)
* Tell the rest of git that any URLs we get don't come
* directly from the user, so it can apply policy as appropriate.
*/
- strvec_push(&cp.env, "GIT_PROTOCOL_FROM_USER=0");
- setup_helper_args(argc, argv, prefix, opt_quiet, opt_cached,
- opt_recursive, &cp.args, options);
+ xsetenv("GIT_PROTOCOL_FROM_USER", "0", 1);
- cp.git_cmd = 1;
- cp.no_stdin = 0; /* for git submodule foreach */
- cp.dir = startup_info->original_cwd;
+ setup_helper_args(argc, argv, prefix, opt_quiet, opt_cached,
+ opt_recursive, &args, options);
- return run_command(&cp);
+ return cmd_submodule_builtin(&args, prefix);
}
--
2.38.0.1091.gf9d18265e59
next prev parent reply other threads:[~2022-10-17 12:10 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 12:09 [PATCH 00/10] submodule: make it a built-in, remove git-submodule.sh Ævar Arnfjörð Bjarmason
2022-10-17 12:09 ` [PATCH 01/10] git-submodule.sh: create a "case" dispatch statement Ævar Arnfjörð Bjarmason
2022-10-17 12:09 ` [PATCH 02/10] git-submodule.sh: dispatch "sync" to helper Ævar Arnfjörð Bjarmason
2022-10-20 20:42 ` Glen Choo
2022-10-17 12:09 ` [PATCH 03/10] git-submodule.sh: dispatch directly " Ævar Arnfjörð Bjarmason
2022-10-17 12:09 ` [PATCH 04/10] git-submodule.sh: dispatch "foreach" " Ævar Arnfjörð Bjarmason
2022-10-20 21:14 ` Glen Choo
2022-10-17 12:09 ` [PATCH 05/10] git-submodule.sh: dispatch "update" " Ævar Arnfjörð Bjarmason
2022-10-20 21:50 ` Glen Choo
2022-10-17 12:09 ` [PATCH 06/10] git-submodule.sh: don't support top-level "--cached" Ævar Arnfjörð Bjarmason
2022-10-20 22:14 ` Glen Choo
2022-10-17 12:09 ` [PATCH 07/10] submodule: make it a built-in, remove git-submodule.sh Ævar Arnfjörð Bjarmason
2022-10-20 22:49 ` Glen Choo
2022-10-17 12:09 ` [PATCH 08/10] submodule: support "--" with no other arguments Ævar Arnfjörð Bjarmason
2022-10-17 12:09 ` [PATCH 09/10] submodule: support sub-command-less "--recursive" option Ævar Arnfjörð Bjarmason
2022-10-20 23:05 ` Glen Choo
2022-10-17 12:09 ` Ævar Arnfjörð Bjarmason [this message]
2022-10-20 23:18 ` [PATCH 10/10] submodule: don't use a subprocess to invoke "submodule--helper" Glen Choo
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