> > Unfortunately this patch didn't make any difference, in fact it hurt > several of the workloads even more. I also tried disabling preemption > when spinning on owner to actually resemble spinlocks, which was my > original plan, yet not much difference. >
That's also similar to the performance I got. There are things about optimistic spinning that I missed that results in the better mutex performance. So I'm scratching my head. > A few ideas that come to mind are avoiding taking the ->wait_lock and > avoid dealing with waiters when doing the optimistic spinning (just like > mutexes do). > For my patch, we actually spin without the wait_lock. > I agree that we should first deal with the optimistic spinning before > adding the MCS complexity. > > > Matthew and I have also discussed possibly introducing some > > limited spinning for writer when semaphore is held by read. > > His idea was to have readers as well as writers set ->owner. > > Writers, as now, unconditionally clear owner. Readers clear > > owner if sem->owner == current. Writers spin on ->owner if ->owner > > is non-NULL and still active. That gives us a reasonable chance > > to spin since we'll be spinning on > > the most recent acquirer of the lock. > > I also tried implementing this concept on top of your patch, didn't make > much of a difference with or without it. > It also didn't make a difference for me. Tim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
