grep: move driver pre-load out of critical section

In builtin/grep.c:add_work() we pre-load the userdiff drivers before
adding the grep_source in the todo list. This operation is currently
being performed after acquiring the grep_mutex, but as it's already
thread-safe, we don't need to protect it here. So let's move it out of
the critical section which should avoid thread contention and improve
performance.

Running[1] `git grep --threads=8 abcd[02] HEAD` on chromium's
repository[2], I got the following mean times for 30 executions after 2
warmups:

        Original         |  6.2886s
-------------------------|-----------
 Out of critical section |  5.7852s

[1]: Tests performed on an i7-7700HQ with 16GB of RAM and SSD, running
     Manjaro Linux.
[2]: chromium’s repo at commit 03ae96f (“Add filters testing at DSF=2”,
         04-06-2019), after a 'git gc' execution.

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/grep.c b/builtin/grep.c
index 6aaa8d44061723db1e5211b6e664b10166e00552..a85b710b48fab6d1e69859d82135d17a255895a0 100644 (file)
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -92,8 +92,11 @@ static pthread_cond_t cond_result;
 
 static int skip_first_line;
 
-static void add_work(struct grep_opt *opt, const struct grep_source *gs)
+static void add_work(struct grep_opt *opt, struct grep_source *gs)
 {
+       if (opt->binary != GREP_BINARY_TEXT)
+               grep_source_load_driver(gs, opt->repo->index);
+
        grep_lock();
 
        while ((todo_end+1) % ARRAY_SIZE(todo) == todo_done) {
@@ -101,9 +104,6 @@ static void add_work(struct grep_opt *opt, const struct grep_source *gs)
        }
 
        todo[todo_end].source = *gs;
-       if (opt->binary != GREP_BINARY_TEXT)
-               grep_source_load_driver(&todo[todo_end].source,
-                                       opt->repo->index);
        todo[todo_end].done = 0;
        strbuf_reset(&todo[todo_end].out);
        todo_end = (todo_end + 1) % ARRAY_SIZE(todo);