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upload-pack: use stdio in send_ref callbacks 

In both protocol v0 and v2, upload-pack writes one pktline packet per
advertised ref to stdout. That means one or two write(2) syscalls per
ref. This is problematic if these writes become network sends with
high overhead.

This commit changes both send_ref callbacks to use buffered IO using
stdio.

To give an example of the impact: I set up a single-threaded loop that
calls ls-remote (with HTTP and protocol v2) on a local GitLab
instance, on a repository with 11K refs. When I switch from Git
v2.32.0 to this patch, I see a 40% reduction in CPU time for Git, and
65% for Gitaly (GitLab's Git RPC service).

So using buffered IO not only saves syscalls in upload-pack, it also
saves time in things that consume upload-pack's output.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jacob Vosmaer <jacob@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jacob Vosmaer 2021-09-01 14:54:42 +02:00 committed by Junio C Hamano
parent 96328398b3
commit 70afef5cdf
2 changed files with 10 additions and 5 deletions
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4
ls-refs.c
View File

@ -105,7 +105,7 @@ static int send_ref(const char *refname, const struct object_id *oid,
}
strbuf_addch(&refline, '\n');
packet_write(1, refline.buf, refline.len);
packet_fwrite(stdout, refline.buf, refline.len);
strbuf_release(&refline);
return 0;
@ -171,7 +171,7 @@ int ls_refs(struct repository *r, struct strvec *keys,
strvec_push(&data.prefixes, "");
for_each_fullref_in_prefixes(get_git_namespace(), data.prefixes.v,
send_ref, &data, 0);
packet_flush(1);
packet_fflush(stdout);
strvec_clear(&data.prefixes);
return 0;
}

11
upload-pack.c
View File

@ -1207,7 +1207,7 @@ static int send_ref(const char *refname, const struct object_id *oid,
format_symref_info(&symref_info, &data->symref);
format_session_id(&session_id, data);
packet_write_fmt(1, "%s %s%c%s%s%s%s%s%s%s object-format=%s agent=%s\n",
packet_fwrite_fmt(stdout, "%s %s%c%s%s%s%s%s%s%s object-format=%s agent=%s\n",
oid_to_hex(oid), refname_nons,
0, capabilities,
(data->allow_uor & ALLOW_TIP_SHA1) ?
@ -1223,11 +1223,11 @@ static int send_ref(const char *refname, const struct object_id *oid,
strbuf_release(&symref_info);
strbuf_release(&session_id);
} else {
packet_write_fmt(1, "%s %s\n", oid_to_hex(oid), refname_nons);
packet_fwrite_fmt(stdout, "%s %s\n", oid_to_hex(oid), refname_nons);
}
capabilities = NULL;
if (!peel_iterated_oid(oid, &peeled))
packet_write_fmt(1, "%s %s^{}\n", oid_to_hex(&peeled), refname_nons);
packet_fwrite_fmt(stdout, "%s %s^{}\n", oid_to_hex(&peeled), refname_nons);
return 0;
}
@ -1348,6 +1348,11 @@ void upload_pack(struct upload_pack_options *options)
reset_timeout(data.timeout);
head_ref_namespaced(send_ref, &data);
for_each_namespaced_ref(send_ref, &data);
/*
* fflush stdout before calling advertise_shallow_grafts because send_ref
* uses stdio.
*/
fflush_or_die(stdout);
advertise_shallow_grafts(1);
packet_flush(1);
} else {