Messages in this thread | | | Date | Thu, 12 Jun 2003 11:04:42 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] io stalls |
| |
Andrea Arcangeli wrote:
>On Wed, Jun 11, 2003 at 02:27:13PM -0400, Chris Mason wrote: > >>On Wed, 2003-06-11 at 14:12, Andrea Arcangeli wrote: >> >>>On Wed, Jun 11, 2003 at 01:42:41PM -0400, Chris Mason wrote: >>> >>>>+ if (q->rq[rw].count >= q->batch_requests) { >>>>+ smp_mb(); >>>>+ if (waitqueue_active(&q->wait_for_requests[rw])) >>>>+ wake_up(&q->wait_for_requests[rw]); >>>> >>>in my tree I also changed this to: >>> >>> wake_up_nr(&q->wait_for_requests[rw], q->rq[rw].count); >>> >>>otherwise only one waiter will eat the requests, while multiple waiters >>>can eat requests in parallel instead because we freed not just 1 request >>>but many of them. >>> >>I tried a few variations of this yesterday and they all led to horrible >>latencies, but I couldn't really explain why. I had a bunch of other >> > >the I/O latency in theory shouldn't change, we're not reordering the >queue at all, they'll go to sleep immediatly again if __get_request >returns null. >
And go to the end of the queue?
> >>stuff in at the time to try and improve throughput though, so I'll try >>it again. >> >>I think part of the problem is the cascading wakeups from >>get_request_wait_wakeup(). So if we wakeup 32 procs they in turn wakeup >>another 32, etc. >> > >so maybe it's enough to wakeup count / 2 to account for the double >wakeup? that will avoid some overscheduling indeed. > >
Andrea, this isn't needed because when the queue falls below the batch limit, every retiring request will do a wake up and another request will be put on (as long as the waitqueue is active).
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |