Messages in this thread | | | From | Josh Don <> | Date | Thu, 14 Oct 2021 16:18:54 -0700 | Subject | Re: [PATCH] sched/core: forced idle accounting |
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On Thu, Oct 14, 2021 at 7:24 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Oct 12, 2021 at 12:45:28PM -0700, Josh Don wrote: > > On Tue, Oct 12, 2021 at 5:27 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > We scale by the number of cpus actually forced idle, since we don't > > > > want to falsely over or under charge forced idle time (defined > > > > strictly as time where we have a runnable task but idle the cpu). The > > > > more important scaling here though is the division over the number of > > > > running entities. This is done so that the aggregate amount of forced > > > > idle over some group of threads makes sense. Ie if we have a cpu with > > > > SMT8, and a group of 7 threads sharing a cookie, we don't want to > > > > accrue 7 units of forced idle time per unit time while the 8th SMT is > > > > forced idle. > > > > > > So why not simply compute the strict per-cpu force-idle time and let > > > userspace sort out the rest? > > > > Do you mean to compute force idle solely as a per-cpu value? I think > > that would be fine in addition to the per-thread field, but a > > desirable property here is proper attribution to the cause of the > > force idle. That lets system management understand which jobs are the > > most antagonistic from a coresched perspective, and is a signal > > (albeit noisy, due to system state and load balancing decisions) for > > scaling their capacity requirements. > > Urgh, reading is hard. I hadn't noticed you did per-task accounting (and > the original changelog doesn't clarify this either).
Yea, I'll add that to the description, along with a few other implementation details.
> Also, should all this be undef SCHED_DEBUG ? Or be part of SCHEDSTATS ?
schedstats seems like a good home, that way users can avoid most of the extra overhead if schedstats is disabled.
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