Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH] block: loop: avoiding too many pending per work I/O | Date | Thu, 30 Apr 2015 12:59:59 -0400 |
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Ming Lei <ming.lei@canonical.com> writes:
> On Wed, Apr 29, 2015 at 12:36 AM, Jeff Moyer <jmoyer@redhat.com> wrote: >> Ming Lei <ming.lei@canonical.com> 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.
Cheers, Jeff
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