Re: Git and GCC

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

On 12/6/07, Nicolas Pitre <nico@cam.org> wrote:
> > When I lasted looked at the code, the problem was in evenly dividing
> > the work. I was using a four core machine and most of the time one
> > core would end up with 3-5x the work of the lightest loaded core.
> > Setting pack.threads up to 20 fixed the problem. With a high number of
> > threads I was able to get a 4hr pack to finished in something like
> > 1:15.
>
> But as far as I know you didn't try my latest incarnation which has been
> available in Git's master branch for a few months already.

I've deleted all my giant packs. Using the kernel pack:
4GB Q6600

Using the current thread pack code I get these results.

The interesting case is the last one. I set it to 15 threads and
monitored with 'top'.
For 0-60% compression I was at 300% CPU, 60-74% was 200% CPU and
74-100% was 100% CPU. It never used all for cores. The only other
things running were top and my desktop. This is the same load
balancing problem I observed earlier. Much more clock time was spent
in the 2/1 core phases than the 3 core one.

Threaded, threads = 5

jonsmirl@terra:/home/linux$ time git repack -a -d -f
Counting objects: 648366, done.
Compressing objects: 100% (647457/647457), done.
Writing objects: 100% (648366/648366), done.
Total 648366 (delta 528994), reused 0 (delta 0)

real    1m31.395s
user    2m59.239s
sys     0m3.048s
jonsmirl@terra:/home/linux$

12 seconds counting
53 seconds compressing
38 seconds writing

Without threads,

jonsmirl@terra:/home/linux$ time git repack -a -d -f
warning: no threads support, ignoring pack.threads
Counting objects: 648366, done.
Compressing objects: 100% (647457/647457), done.
Writing objects: 100% (648366/648366), done.
Total 648366 (delta 528999), reused 0 (delta 0)

real    2m54.849s
user    2m51.267s
sys     0m1.412s
jonsmirl@terra:/home/linux$

Threaded, threads = 5

jonsmirl@terra:/home/linux$ 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 539080), reused 0 (delta 0)

real    9m18.032s
user    19m7.484s
sys     0m3.880s
jonsmirl@terra:/home/linux$

jonsmirl@terra:/home/linux/.git/objects/pack$ ls -l
total 182156
-r--r--r-- 1 jonsmirl jonsmirl  15561848 2007-12-06 16:15
pack-f1f8637d2c68eb1c964ec7c1877196c0c7513412.idx
-r--r--r-- 1 jonsmirl jonsmirl 170768761 2007-12-06 16:15
pack-f1f8637d2c68eb1c964ec7c1877196c0c7513412.pack
jonsmirl@terra:/home/linux/.git/objects/pack$

Non-threaded:

jonsmirl@terra:/home/linux$ time git repack -a -d -f --depth=250 --window=250
warning: no threads support, ignoring pack.threads
Counting objects: 648366, done.
Compressing objects: 100% (647457/647457), done.
Writing objects: 100% (648366/648366), done.
Total 648366 (delta 539080), reused 0 (delta 0)

real    18m51.183s
user    18m46.538s
sys     0m1.604s
jonsmirl@terra:/home/linux$


jonsmirl@terra:/home/linux/.git/objects/pack$ ls -l
total 182156
-r--r--r-- 1 jonsmirl jonsmirl  15561848 2007-12-06 15:33
pack-f1f8637d2c68eb1c964ec7c1877196c0c7513412.idx
-r--r--r-- 1 jonsmirl jonsmirl 170768761 2007-12-06 15:33
pack-f1f8637d2c68eb1c964ec7c1877196c0c7513412.pack
jonsmirl@terra:/home/linux/.git/objects/pack$

Threaded, threads = 15

jonsmirl@terra:/home/linux$ 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 539080), reused 0 (delta 0)

real    9m18.325s
user    19m14.340s
sys     0m3.996s
jonsmirl@terra:/home/linux$

-- 
Jon Smirl
jonsmirl@gmail.com