Re: [PATCH v2] pack-objects: Use packing_data lock instead of read_mutex

From: Duy Nguyen <pclouds@gmail.com>
Date: Jan 22, 2019, 10:25 UTC
Message-ID: <CACsJy8Cdc-AcPDRquxHu-LmHUjzHmR2GEmARbnPcwXgjp8+HMQ@mail.gmail.com>
In-Reply-To: <20190122072809.GA28975@sigill.intra.peff.net>

On Tue, Jan 22, 2019 at 2:28 PM Jeff King <peff@peff.net> wrote:

Show 21 quoted lines

>
> On Mon, Jan 21, 2019 at 05:02:33PM +0700, Duy Nguyen wrote:
>
> > > As I mentioned in the prior thread I think that it will be simpler
> > > to simply use the existing lock in packing_data instead of moving
> > > read_mutex. I can go back to simply moving read_mutex to the
> > > packing_data struct if that that is preferable, though.
> >
> > In early iterations of these changes, I think we hit high contention
> > when sharing the mutex [1]. I don't know if we will hit the same
> > performance problem again with this patch. It would be great if Elijah
> > with his zillion core machine could test this out. Otherwise it may be
> > just safer to keep the two mutexes separate.
> >
> > [1] http://public-inbox.org/git/20180720052829.GA3852@sigill.intra.peff.net/
>
> I haven't been following this thread closely, but I still have access to
> a 40-core machine if you'd like me to time anything.
>
> It sounds like _this_ patch is the more fine-grained one. Is the more
> coarse-grained one already written?

A more fine-grained one would be 'master' where we use two separate mutexes for different code. I guess if repack performance with this patch is still the same as 'master', we're good to go. You may need to lower $GIT_TEST_OE_SIZE and $GIT_TEST_OE_DELTA_SIZE to force more lock contention.

-- 
Duy