From: Nicolas Pitre Date: Thu, 06 Dec 2007 19:08:12 GMT Subject: Re: Git and GCC Message-ID: In-Reply-To: <9e4733910712061055p353775d8wd0321bc9c81297b7@mail.gmail.com> On Thu, 6 Dec 2007, Jon Smirl wrote: > On 12/6/07, Linus Torvalds wrote: > > > > > > On Thu, 6 Dec 2007, Jeff King wrote: > > > > > > What is really disappointing is that we saved only about 20% of the > > > time. I didn't sit around watching the stages, but my guess is that we > > > spent a long time in the single threaded "writing objects" stage with a > > > thrashing delta cache. > > > > I don't think you spent all that much time writing the objects. That part > > isn't very intensive, it's mostly about the IO. > > > > I suspect you may simply be dominated by memory-throughput issues. The > > delta matching doesn't cache all that well, and using two or more cores > > isn't going to help all that much if they are largely waiting for memory > > (and quite possibly also perhaps fighting each other for a shared cache? > > Is this a Core 2 with the shared L2?) > > 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. Nicolas