Re: Git and GCC

From: Jon Smirl <jonsmirl@gmail.com>
Date: Dec 6, 2007, 21:39 UTC
Message-ID: <9e4733910712061339n3aef023r22e5b73aac120c8a@mail.gmail.com>
In-Reply-To: <alpine.LFD.0.99999.0712061403000.555@xanadu.home>

On 12/6/07, Nicolas Pitre <nico@cam.org> wrote:

Show 9 quoted lines

> > 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

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

-- 
Jon Smirl
jonsmirl@gmail.com