Merge branch 'ps/upload-pack-buffer-more-writes'

Reduce system overhead "git upload-pack" spends on relaying "git
pack-objects" output to the "git fetch" running on the other end of
the connection.

* ps/upload-pack-buffer-more-writes:
  builtin/pack-objects: reduce lock contention when writing packfile data
  csum-file: drop `hashfd_throughput()`
  csum-file: introduce `hashfd_ext()`
  sideband: use writev(3p) to send pktlines
  wrapper: introduce writev(3p) wrappers
  compat/posix: introduce writev(3p) wrapper
  upload-pack: reduce lock contention when writing packfile data
  upload-pack: prefer flushing data over sending keepalive
  upload-pack: adapt keepalives based on buffering
  upload-pack: fix debug statement when flushing packfile data

1 files changed, 19 insertions, 4 deletions

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index cd013c0b68..da1087930c 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -41,6 +41,7 @@
 #include "promisor-remote.h"
 #include "pack-mtimes.h"
 #include "parse-options.h"
+#include "pkt-line.h"
 #include "blob.h"
 #include "tree.h"
 #include "path-walk.h"
@@ -1330,11 +1331,25 @@ static void write_pack_file(void)
 		unsigned char hash[GIT_MAX_RAWSZ];
 		char *pack_tmp_name = NULL;
 
-		if (pack_to_stdout)
-			f = hashfd_throughput(the_repository->hash_algo, 1,
-					      "<stdout>", progress_state);
-		else
+		if (pack_to_stdout) {
+			/*
+			 * This command is most often invoked via
+			 * git-upload-pack(1), which will typically chunk data
+			 * into pktlines. As such, we use the maximum data
+			 * length of them as buffer length.
+			 *
+			 * Note that we need to subtract one though to
+			 * accomodate for the sideband byte.
+			 */
+			struct hashfd_options opts = {
+				.progress = progress_state,
+				.buffer_len = LARGE_PACKET_DATA_MAX - 1,
+			};
+			f = hashfd_ext(the_repository->hash_algo, 1,
+				       "<stdout>", &opts);
+		} else {
 			f = create_tmp_packfile(the_repository, &pack_tmp_name);
+		}
 
 		offset = write_pack_header(f, nr_remaining);