Messages in this thread | | | Date | Sun, 25 Feb 2001 18:34:01 +0100 | From | Jens Axboe <> | Subject | Re: ll_rw_block/submit_bh and request limits |
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On Thu, Feb 22 2001, Andrea Arcangeli wrote: > On Thu, Feb 22, 2001 at 10:59:20AM -0800, Linus Torvalds wrote: > > I'd prefer for this check to be a per-queue one. > > I'm running this in my tree since a few weeks, however I never had the courage > to post it publically because I didn't benchmarked it carefully yet and I > prefer to finish another thing first. This is actually based on the code I had > in my blkdev tree after I merged last time with Jens the 512K I/O requests and > elevator fixes. I think it won't generate bad numbers and it was running fine > on a 32way SMP (though I didn't stressed the I/O subsystem much there) but > please don't include until somebody benchmarks it carefully with dbench and > tiotest. (it still applys cleanly against 2.4.2)
Thinking about this a bit, I have to agree with you and Linus. It is possible to find pathetic cases where the per-queue limit suffers compared to the global one, but in reality I don't think it's worth it. And the per-queue limits saves us the atomic updates since it's done under the io_request_lock (or queue later, still fine) so that's a win too.
I have had rw wait queues before, was removed when I did the request stealing which is now gone again. I'm not even sure it's worth it now, Marcelo and I discussed it last week and I did some tests that showed nothing remarkable. But it's mainly for free, so we might as well do it.
Any reason why you don't have a lower wake-up limit for the queue? Do you mind if I do some testing with this patch and fold it in, possibly?
-- Jens Axboe
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