Re: Git and GCC

["Jon Smirl" <jonsmirl@gmail.com>]

On 12/6/07, Nicolas Pitre <nico@cam.org> wrote:
> > > Well, that's possible with a window 25 times larger than the default.
> >
> > Why did it never use more than three cores?
>
> You have 648366 objects total, and only 647457 of them are subject to
> delta compression.
>
> With a window size of 250 and a default thread segment of window * 1000
> that means only 3 segments will be distributed to threads, hence only 3
> threads with work to do.

One little tweak and the clock time drops from 9.5 to 6 minutes. The
tweak makes all four cores work.

jonsmirl@terra:/home/apps/git$ git diff
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 4f44658..e0dd12e 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1645,7 +1645,7 @@ static void ll_find_deltas(struct object_entry
**list, unsigned list_size,
        }

        /* this should be auto-tuned somehow */
-       chunk_size = window * 1000;
+       chunk_size = window * 50;

        do {
                unsigned sublist_size = chunk_size;


jonsmirl@terra:/home/linux/.git$ time git repack -a -d -f --depth=250
--window=250
Counting objects: 648366, done.
Compressing objects: 100% (647457/647457), done.
Writing objects: 100% (648366/648366), done.
Total 648366 (delta 539043), reused 0 (delta 0)

real    6m2.109s
user    20m0.491s
sys     0m4.608s
jonsmirl@terra:/home/linux/.git$



>
>
> Nicolas
>


-- 
Jon Smirl
jonsmirl@gmail.com