Re: [PATCH 0/8 v3] bfq: Limit number of allocated scheduler tags per cgroup

Jan Kara
2021-10-25T11:14:53Z

On Mon 25-10-21 09:58:11, Paolo Valente wrote:
> > Il giorno 7 ott 2021, alle ore 18:33, Paolo Valente <paolo.valente@linaro.org> ha scritto:
> >> Il giorno 6 ott 2021, alle ore 19:31, Jan Kara <jack@suse.cz> ha scritto:
> >>
> >> Hello!
> >>
> >> Here is the third revision of my patches to fix how bfq weights apply on cgroup
> >> throughput and on throughput of processes with different IO priorities. Since
> >> v2 I've added some more patches so that now IO priorities also result in
> >> service differentiation (previously they had no effect on service
> >> differentiation on some workloads similarly to cgroup weights). The last patch
> >> in the series still needs some work as in the current state it causes a
> >> notable regression (~20-30%) with dbench benchmark for large numbers of
> >> clients. I've verified that the last patch is indeed necessary for the service
> >> differentiation with the workload described in its changelog. As we discussed
> >> with Paolo, I have also found out that if I remove the "waker has enough
> >> budget" condition from bfq_select_queue(), dbench performance is restored
> >> and the service differentiation is still good. But we probably need some
> >> justification or cleaner solution than just removing the condition so that
> >> is still up to discussion. But first seven patches already noticeably improve
> >> the situation for lots of workloads so IMO they stand on their own and
> >> can be merged regardless of how we go about the last patch.
> >>
> >
> > Hi Jan,
> > I have just one more (easy-to-resolve) doubt: you seem to have tested
> > these patches mostly on the throughput side. Did you run a
> > startup-latency test as well? I can run some for you, if you prefer
> > so. Just give me a few days.
> >
>
> We are finally testing your patches a little bit right now, for
> regressions with our typical benchmarks ...

Hum, strange I didn't get your previous email about benchmarks. You're
right I didn't run startup-latency AFAIR. Now that you've started them,
probably there's no big point in me queuing them as well. So thanks for
the benchmarking :)

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR