Re: performance on repack

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

On 8/15/07, Nicolas Pitre <nico@cam.org> wrote:
> On Wed, 15 Aug 2007, Jon Smirl wrote:
>
> > On 8/15/07, Martin Koegler <mkoegler@auto.tuwien.ac.at> wrote:
> > > git-pack-objects knows the order, in which it will use the objects.  A
> > > seperate thread could pre-read the next object and wait until the main
> > > thread starts processing it. After the read is complete, another
> > > thread could start computing the delta index.
> >
> > The hope is that the new adaptive read ahead code in the kernel will
> > get this right and you won't need the second thread. Letting the
> > kernel handle the read ahead will dynamically scale as other demands
> > are made on the host. There's effectively only one read ahead cache in
> > the system, only the kernel really knows how to divide it up between
> > competing apps.
>
> No read ahead will ever help the delta search phase.  Objects listed for
> deltification against each other are sorted in a way that results in
> reads from completely random location in the object store.
>
> Normally the delta search phase is so compute intensive that the read
> shouldn't matter much.

I agree, I am compute bound for 20 min, disk light occasionally dimly flickers.

Besides, the main thread that is preparing the queue effectively
functions as a read ahead thread. It will overlap with the compute
bound delta searches.

>
>
> Nicolas
>


-- 
Jon Smirl
jonsmirl@gmail.com