threaded delta search: specify number of threads at run time

This adds a --threads=<n> parameter to 'git pack-objects' with
documentation.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-pack-objects.txt b/Documentation/git-pack-objects.txt
index 6f17cff24ab784ee68767724dff6892b67b3ad53..f9b97956e36363504192056953d137c0f517f27d 100644 (file)
--- a/Documentation/git-pack-objects.txt
+++ b/Documentation/git-pack-objects.txt
@@ -173,6 +173,14 @@ base-name::
        length, this option typically shrinks the resulting
        packfile by 3-5 per-cent.
 
+--threads=<n>::
+       Specifies the number of threads to spawn when searching for best
+       delta matches.  This requires that pack-objects be compiled with
+       pthreads otherwise this option is ignored with a warning.
+       This is meant to reduce packing time on multiprocessor machines.
+       The required amount of memory for the delta search window is
+       however multiplied by the number of threads.
+
 --index-version=<version>[,<offset>]::
        This is intended to be used by the test suite only. It allows
        to force the version for the generated pack index, and to force

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index b13558ee7ea2623d426bc4af7787e3e488990dda..42698d29486390f4aef727ef5771d87a95dbbfcc 100644 (file)
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -24,7 +24,7 @@ git-pack-objects [{ -q | --progress | --all-progress }] \n\
        [--max-pack-size=N] [--local] [--incremental] \n\
        [--window=N] [--window-memory=N] [--depth=N] \n\
        [--no-reuse-delta] [--no-reuse-object] [--delta-base-offset] \n\
-       [--non-empty] [--revs [--unpacked | --all]*] [--reflog] \n\
+       [--threads=N] [--non-empty] [--revs [--unpacked | --all]*] [--reflog] \n\
        [--stdout | base-name] [<ref-list | <object-list]";
 
 struct object_entry {
@@ -72,6 +72,7 @@ static int progress = 1;
 static int window = 10;
 static uint32_t pack_size_limit;
 static int depth = 50;
+static int delta_search_threads = 1;
 static int pack_to_stdout;
 static int num_preferred_base;
 static struct progress progress_state;
@@ -1605,19 +1606,22 @@ static void *threaded_find_deltas(void *arg)
        }
 }
 
-#define NR_THREADS     4
-
 static void ll_find_deltas(struct object_entry **list, unsigned list_size,
                           int window, int depth, unsigned *processed)
 {
-       struct thread_params p[NR_THREADS];
+       struct thread_params p[delta_search_threads];
        int i, ret;
        unsigned chunk_size;
 
+       if (delta_search_threads <= 1) {
+               find_deltas(list, list_size, window, depth, processed);
+               return;
+       }
+
        pthread_mutex_lock(&data_provider);
        pthread_mutex_lock(&data_ready);
 
-       for (i = 0; i < NR_THREADS; i++) {
+       for (i = 0; i < delta_search_threads; i++) {
                p[i].window = window;
                p[i].depth = depth;
                p[i].processed = processed;
@@ -1900,6 +1904,18 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
                                usage(pack_usage);
                        continue;
                }
+               if (!prefixcmp(arg, "--threads=")) {
+                       char *end;
+                       delta_search_threads = strtoul(arg+10, &end, 0);
+                       if (!arg[10] || *end || delta_search_threads < 1)
+                               usage(pack_usage);
+#ifndef THREADED_DELTA_SEARCH
+                       if (delta_search_threads > 1)
+                               warning("no threads support, "
+                                       "ignoring %s", arg);
+#endif
+                       continue;
+               }
                if (!prefixcmp(arg, "--depth=")) {
                        char *end;
                        depth = strtoul(arg+8, &end, 0);