Messages in this thread | | | Date | Tue, 21 Mar 2023 15:21:12 +0200 (EET) | From | Ilpo Järvinen <> | Subject | Re: [PATCH v3 08/19] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow |
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On Mon, 20 Mar 2023, 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 houskeeping CPU is > available. > > Signed-off-by: James Morse <james.morse@arm.com> > --- > arch/x86/kernel/cpu/resctrl/internal.h | 23 +++++++++++++++++++++++ > arch/x86/kernel/cpu/resctrl/monitor.c | 17 ++++++++++++----- > include/linux/tick.h | 3 ++- > 3 files changed, 37 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h > index 87545e4beb70..0b5fd5a0cda2 100644 > --- a/arch/x86/kernel/cpu/resctrl/internal.h > +++ b/arch/x86/kernel/cpu/resctrl/internal.h > @@ -7,6 +7,7 @@ > #include <linux/kernfs.h> > #include <linux/fs_context.h> > #include <linux/jump_label.h> > +#include <linux/tick.h> > #include <asm/resctrl.h> > > #define L3_QOS_CDP_ENABLE 0x01ULL > @@ -55,6 +56,28 @@ > /* Max event bits supported */ > #define MAX_EVT_CONFIG_BITS GENMASK(6, 0) > > +/** > + * cpumask_any_housekeeping() - Chose any cpu in @mask, preferring those that
Choose
> + * aren't marked nohz_full > + * @mask: The mask to pick a CPU from. > + * > + * Returns a CPU in @mask. If there are houskeeping CPUs that don't use
housekeeping
> + * nohz_full, these are preferred. > + */ > +static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask) > +{ > + int cpu, hk_cpu; > + > + cpu = cpumask_any(mask); > + if (tick_nohz_full_cpu(cpu)) { > + hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask); > + if (hk_cpu < nr_cpu_ids) > + cpu = hk_cpu; > + } > + > + return cpu; > +} > + > struct rdt_fs_context { > struct kernfs_fs_context kfc; > bool enable_cdpl2; > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c > index a2ae4be4b2ba..3bec5c59ca0e 100644 > --- a/arch/x86/kernel/cpu/resctrl/monitor.c > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c > @@ -745,9 +745,9 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, > void cqm_handle_limbo(struct work_struct *work) > { > unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL); > - int cpu = smp_processor_id(); > struct rdt_resource *r; > struct rdt_domain *d; > + int cpu; > > mutex_lock(&rdtgroup_mutex); > > @@ -756,8 +756,10 @@ void cqm_handle_limbo(struct work_struct *work) > > __check_limbo(d, false); > > - if (has_busy_rmid(r, d)) > + if (has_busy_rmid(r, d)) { > + cpu = cpumask_any_housekeeping(&d->cpu_mask); > schedule_delayed_work_on(cpu, &d->cqm_limbo, delay); > + } > > mutex_unlock(&rdtgroup_mutex); > } > @@ -767,7 +769,7 @@ void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms) > unsigned long delay = msecs_to_jiffies(delay_ms); > int cpu; > > - cpu = cpumask_any(&dom->cpu_mask); > + cpu = cpumask_any_housekeeping(&dom->cpu_mask); > dom->cqm_work_cpu = cpu; > > schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay); > @@ -777,10 +779,10 @@ void mbm_handle_overflow(struct work_struct *work) > { > unsigned long delay = msecs_to_jiffies(MBM_OVERFLOW_INTERVAL); > struct rdtgroup *prgrp, *crgrp; > - int cpu = smp_processor_id(); > struct list_head *head; > struct rdt_resource *r; > struct rdt_domain *d; > + int cpu; > > mutex_lock(&rdtgroup_mutex); > > @@ -801,6 +803,11 @@ void mbm_handle_overflow(struct work_struct *work) > update_mba_bw(prgrp, d); > } > > + /* > + * Re-check for housekeeping CPUs. This allows the overflow handler to > + * move off a nohz_full CPU quickly. > + */ > + cpu = cpumask_any_housekeeping(&d->cpu_mask); > schedule_delayed_work_on(cpu, &d->mbm_over, delay); > > out_unlock: > @@ -814,7 +821,7 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms) > > if (!static_branch_likely(&rdt_mon_enable_key)) > return; > - cpu = cpumask_any(&dom->cpu_mask); > + cpu = cpumask_any_housekeeping(&dom->cpu_mask); > dom->mbm_work_cpu = cpu; > schedule_delayed_work_on(cpu, &dom->mbm_over, delay); > } > diff --git a/include/linux/tick.h b/include/linux/tick.h > index bfd571f18cfd..ae2e9019fc18 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -174,9 +174,10 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } > static inline void tick_nohz_idle_stop_tick_protected(void) { } > #endif /* !CONFIG_NO_HZ_COMMON */ > > +extern cpumask_var_t tick_nohz_full_mask; > + > #ifdef CONFIG_NO_HZ_FULL > extern bool tick_nohz_full_running; > -extern cpumask_var_t tick_nohz_full_mask;
Its definition seems to also be inside #ifdef:
kernel/time/tick-sched.c-#ifdef CONFIG_NO_HZ_FULL kernel/time/tick-sched.c:cpumask_var_t tick_nohz_full_mask; kernel/time/tick-sched.c:EXPORT_SYMBOL_GPL(tick_nohz_full_mask);
-- i.
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