Messages in this thread | | | Date | Thu, 12 Jun 2003 12:49:46 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] io stalls |
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Andrea Arcangeli wrote:
>On Thu, Jun 12, 2003 at 12:41:58PM +1000, Nick Piggin wrote: > >> >>Chris Mason wrote: >> >> >>>On Wed, 2003-06-11 at 21:29, Andrea Arcangeli wrote: >>> >>> >>> >>>>this will avoid get_request_wait_wakeup to mess the wakeup, so we can >>>>wakep_nr(rq.count) safely. >>>> >>>>then there's the last issue raised by Chris, that is if we get request >>>>released faster than the tasks can run, still we can generate a not >>>>perfect fairness. My solution to that is to change wake_up to have a >>>>nr_exclusive not obeying to the try_to_wakeup retval. that should >>>>guarantee exact FIFO then, but it's a minor issue because the requests >>>>shouldn't be released systematically in a flood. So I'm leaving it >>>>opened for now, the others already addressed should be the major ones. >>>> >>>> >>>I think the only time we really need to wakeup more than one waiter is >>>when we hit the q->batch_request mark. After that, each new request >>>that is freed can be matched with a single waiter, and we know that any >>>previously finished requests have probably already been matched to their >>>own waiter. >>> >>> >>> >>Nope. Not even then. Each retiring request should submit >>a wake up, and the process will submit another request. >>So the number of requests will be held at the batch_request >>mark until no more waiters. >> >>Now that begs the question, why have batch_requests anymore? >>It no longer does anything. >> > >it does nothing w/ _exclusive and w/o the wake_up_nr, that's why I added >the wake_up_nr. > > That is pretty pointless as well. You might as well just start waking up at the queue full limit, and wake one at a time.
The purpose for batch_requests was I think for devices with a very small request size, to reduce context switches.
>Andrea > > >
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