git-for-windows/git
1
0
Fork 0
mirror of https://github.com/git-for-windows/git.git synced 2026-04-11 01:53:21 -05:00
Code Issues Packages Projects Releases 335 Wiki Activity

sideband: use writev(3p) to send pktlines

Browse Source 
Every pktline that we send out via `send_sideband()` currently requires
two syscalls: one to write the pktline's length, and one to send its
data. This typically isn't all that much of a problem, but under extreme
load the syscalls may cause contention in the kernel.

Refactor the code to instead use the newly introduced writev(3p) infra
so that we can send out the data with a single syscall. This reduces the
number of syscalls from around 133,000 calls to write(3p) to around
67,000 calls to writev(3p).

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt
2026-03-13 07:45:18 +01:00
committed by Junio C Hamano
parent 1970fcef93
commit 26986f4cba
1 changed files with 11 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
sideband.c
View File

@@ -264,6 +264,7 @@ void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_ma
const char *p = data;
while (sz) {
struct iovec iov[2];
unsigned n;
char hdr[5];
@@ -273,12 +274,19 @@ void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_ma
if (0 <= band) {
xsnprintf(hdr, sizeof(hdr), "%04x", n + 5);
hdr[4] = band;
write_or_die(fd, hdr, 5);
iov[0].iov_base = hdr;
iov[0].iov_len = 5;
} else {
xsnprintf(hdr, sizeof(hdr), "%04x", n + 4);
write_or_die(fd, hdr, 4);
iov[0].iov_base = hdr;
iov[0].iov_len = 4;
}
write_or_die(fd, p, n);
iov[1].iov_base = (void *) p;
iov[1].iov_len = n;
writev_or_die(fd, iov, ARRAY_SIZE(iov));
p += n;
sz -= n;
}