Ingo Molnar <[EMAIL PROTECTED]> wrote: > > > ooh, I'd rather not. I spent an intense three days removing all the > > sleeping locks from ext3 (and three months debugging the result). > > Ended up gaining 1000% on 16-way. > > > > Putting them back in will really hurt the SMP performance. > > ah. Yeah. Sniff. > > if we gain 1000% on a 16-way then there's something really wrong about > semaphores (or scheduling) though. A semaphore is almost a spinlock, in > the uncontended case - and even under contention we really (should) just > spend the cycles that we'd spend spinning. There will be some > intermediate contention level where semaphores hurt, but 1000% sounds > truly excessive.
I forget how much of the 1000% came from that, but it was quite a lot. Removing the BKL was the first step. That took the context switch rate under high load from ~10,000/sec up to ~300,000/sec. Because the first thing a CPU hit on entry to the fs was then a semaphore. Performance rather took a dive. Of course the locks also became much finer-grained, so the contention opportunities lessened. But j_list_lock and j_state_lock have fs-wide scope, so I'd expect the context switch rate to go up quite a lot again. The hold times are short, and a context switch hurts rather ore than a quick spin. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
