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,
-- Jens Axboe
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