On Mon, 2008-09-08 at 08:07 -0700, Stephen Hemminger wrote: > On Mon, 8 Sep 2008 16:20:52 +0200 > Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > > > On Mon, Sep 08, 2008 at 10:02:30AM -0400, Chris Mason wrote: > > > On Mon, 2008-09-08 at 15:54 +0200, Andi Kleen wrote: > > > > > The idea is to try to spin for a bit to avoid scheduling away, which is > > > > > especially important for the high levels. Most holders of the mutex > > > > > let it go very quickly. > > > > > > > > Ok but that surely should be implemented in the general mutex code then > > > > or at least in a standard adaptive mutex wrapper? > > > > > > That depends, am I the only one crazy enough to think its a good idea? > > > > Adaptive mutexes are classic, a lot of other OS have it. > > The problem is that they are a nuisance. It is impossible to choose > the right trade off between spin an no-spin, also they optimize for > a case that doesn't occur often enough to be justified. > > People seem to repeatedly come up with adaptive mutex based on intuitive > hunch, and never do much analysis before or afterwards. > In my case, it very easy to measure. Just watch the context switch rate on any metadata intensive workload. The current code scores higher on benchmarks and uses less system time overall. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
