Re: [PATCH] block: loop: avoiding too many pending per work I/O

From: Ming Lei
Date: Thu Apr 30 2015 - 21:21:08 EST

On Fri, May 1, 2015 at 12:59 AM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> Ming Lei <ming.lei@xxxxxxxxxxxxx> writes:
>> On Wed, Apr 29, 2015 at 12:36 AM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
>>> Ming Lei <ming.lei@xxxxxxxxxxxxx> writes:
>>>> If there are too many pending per work I/O, too many
>>>> high priority work thread can be generated so that
>>>> system performance can be effected.
>>>> This patch limits the max pending per work I/O as 16,
>>>> and will fackback to single queue mode when the max
>>>> number is reached.
>>> Actually, it limits it to 32. Also, there is no discussion on what
>>> variables might affect this number. Will that magic number change
>>> depending on the number of cpus on the system, for example?
>> My fault, it should have been 16.
>> It is just used to keep more IOs in flight, but can't cause obvious
>> costs like the case of Fedora live booting.
>> IMO, it shouldn't depend much on number of CPUs, and more
>> related with I/O performance of the backing file, and the number
>> is like 'iodepth' of fio.
> OK, that makes more sense. I'm still not a huge fan of hard-coding
> numbers that are storage-specific, but I don't have a better suggestion
> at the moment, either.

OK, thanks for your review.
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