Messages in this thread | | | Date | Thu, 5 Oct 2023 18:07:14 +0100 | Subject | Re: [PATCH v6 12/24] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow | From | James Morse <> |
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Hi Reinette,
On 03/10/2023 22:15, Reinette Chatre wrote: > On 9/14/2023 10:21 AM, James Morse wrote: >> The limbo and overflow code picks a CPU to use from the domain's list >> of online CPUs. Work is then scheduled on these CPUs to maintain >> the limbo list and any counters that may overflow. >> >> cpumask_any() may pick a CPU that is marked nohz_full, which will >> either penalise the work that CPU was dedicated to, or delay the >> processing of limbo list or counters that may overflow. Perhaps >> indefinitely. Delaying the overflow handling will skew the bandwidth >> values calculated by mba_sc, which expects to be called once a second. >> >> Add cpumask_any_housekeeping() as a replacement for cpumask_any() >> that prefers housekeeping CPUs. This helper will still return >> a nohz_full CPU if that is the only option. The CPU to use is >> re-evaluated each time the limbo/overflow work runs. This ensures >> the work will move off a nohz_full CPU once a housekeeping CPU is >> available.
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c >> index 0bbed8c62d42..993837e46db1 100644 >> --- a/arch/x86/kernel/cpu/resctrl/monitor.c >> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -793,8 +793,10 @@ void cqm_handle_limbo(struct work_struct *work) >> >> __check_limbo(d, false); >> >> - if (has_busy_rmid(d)) >> + if (has_busy_rmid(d)) { >> + cpu = cpumask_any_housekeeping(&d->cpu_mask); >> schedule_delayed_work_on(cpu, &d->cqm_limbo, delay); >> + } >> > > ok - but if you do change the CPU the worker is running on then > I also expect d->cqm_work_cpu to be updated. Otherwise the offline > code will not be able to determine if the worker needs to move.
Good point - I missed this.
Thanks,
James
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