| Message ID | 20221127141742.1644023-3-qyousef@layalina.io (mailing list archive) |
|---|---|
| State | Handled Elsewhere, archived |
| Headers | show |
| Series | Fixes for uclamp and capacity inversion detection | expand |
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?
On 12/01/22 23:39, Dietmar Eggemann wrote: > 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. Aargh > > > + > > 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. Thanks for confirming! > > > 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 Is this directed to me? > 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? If yes, I did answer that here https://lore.kernel.org/lkml/20221120213013.t67xisvqxmftri52@airbuntu/ Thanks a lot Dietmar! -- Qais Yousef
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()); + 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; + cpu = cpumask_any(pd_span); pd_cap_orig = arch_scale_cpu_capacity(cpu);
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(-)