Messages in this thread | | | Date | Thu, 1 Dec 2022 23:39:46 +0100 | Subject | Re: [PATCH 2/3] sched/fair: Fixes for capacity inversion detection | From | Dietmar Eggemann <> |
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On 27/11/2022 15:17, Qais Yousef wrote: > Traversing the Perf Domains requires rcu_read_lock() to be held and is > conditional on sched_energy_enabled(). rcu_read_lock() is held while in > load_balance(), add an assert to ensure this is always the case. > > Also skip capacity inversion detection for our own pd; which was an > error. > > Fixes: 44c7b80bffc3 ("sched/fair: Detect capacity inversion") > Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> > --- > kernel/sched/fair.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 89dadaafc1ec..7c0dd57e562a 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8856,16 +8856,22 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu) > * * Thermal pressure will impact all cpus in this perf domain > * equally. > */ > - if (static_branch_unlikely(&sched_asym_cpucapacity)) { > + if (sched_energy_enabled()) { > unsigned long inv_cap = capacity_orig - thermal_load_avg(rq); > struct perf_domain *pd = rcu_dereference(rq->rd->pd); > > rq->cpu_capacity_inverted = 0; > > + SCHED_WARN_ON(!rcu_read_lock_held());
This will trigger in CPU hotplug via build_sched_domains() -> update_group_capacity() -> update_cpu_capacity() on an EAS system.
> + > for (; pd; pd = pd->next) { > struct cpumask *pd_span = perf_domain_span(pd); > unsigned long pd_cap_orig, pd_cap; > > + /* We can't be inverted against our own pd */ > + if (cpumask_test_cpu(cpu_of(rq), pd_span)) > + continue; > +
This should fix the issue with `cpu` function parameter in its own PD.
> cpu = cpumask_any(pd_span); > pd_cap_orig = arch_scale_cpu_capacity(cpu); >
I still don't get the benefit of the CPU capacity inversion patches in tip/sched/core which should be fixed by this patch:
aa69c36f31aa - sched/fair: Consider capacity inversion in util_fits_cpu() 44c7b80bffc3 - sched/fair: Detect capacity inversion
I have to ask again. Why should we use thermal_load_avg() instead of arch_scale_thermal_pressure() for a CPUx in `CPU capacity inversion state` (i.e. w/ higher `CPU capacity orig` but lower `CPU capacity` than CPUy?
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