Messages in this thread Patch in this message | | | Date | Wed, 30 Oct 2019 14:31:30 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] timers/nohz: Update nohz load even if tick already stopped |
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On Wed, Oct 30, 2019 at 03:48:26AM -0500, Scott Wood wrote: > On Tue, 2019-10-29 at 11:05 +0100, Peter Zijlstra wrote:
> > @@ -3686,6 +3688,7 @@ static void sched_tick_remote(struct work_struct > > *work) > > curr->sched_class->task_tick(rq, curr, 0); > > > > out_unlock: > > + calc_load_nohz_remote(cpu); > > rq_unlock_irq(rq, &rf); > > This gets skipped when the cpu is idle, so it still misses the update.
Oh argh! that's a bit radical of the remote tick. The normal tick runs just fine on idle CPUs, so lets mirror that.
How's this then?
--- diff --git a/include/linux/sched/nohz.h b/include/linux/sched/nohz.h index 1abe91ff6e4a..6d67e9a5af6b 100644 --- a/include/linux/sched/nohz.h +++ b/include/linux/sched/nohz.h @@ -15,9 +15,11 @@ static inline void nohz_balance_enter_idle(int cpu) { } #ifdef CONFIG_NO_HZ_COMMON void calc_load_nohz_start(void); +void calc_load_nohz_remote(struct rq *rq); void calc_load_nohz_stop(void); #else static inline void calc_load_nohz_start(void) { } +static inline void calc_load_nohz_remote(struct rq *rq) { } static inline void calc_load_nohz_stop(void) { } #endif /* CONFIG_NO_HZ_COMMON */ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index eb42b71faab9..d02d1b8f40af 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3660,21 +3660,17 @@ static void sched_tick_remote(struct work_struct *work) u64 delta; int os; - /* - * Handle the tick only if it appears the remote CPU is running in full - * dynticks mode. The check is racy by nature, but missing a tick or - * having one too much is no big deal because the scheduler tick updates - * statistics and checks timeslices in a time-independent way, regardless - * of when exactly it is running. - */ - if (idle_cpu(cpu) || !tick_nohz_tick_stopped_cpu(cpu)) + if (!tick_nohz_tick_stopped_cpu(cpu)) goto out_requeue; rq_lock_irq(rq, &rf); - curr = rq->curr; - if (is_idle_task(curr) || cpu_is_offline(cpu)) + /* + * We must not call calc_load_nohz_remote() when not in NOHZ mode. + */ + if (cpu_is_offline(cpu) || !tick_nohz_tick_stopped(cpu)) goto out_unlock; + curr = rq->curr; update_rq_clock(rq); delta = rq_clock_task(rq) - curr->se.exec_start; @@ -3685,10 +3681,11 @@ static void sched_tick_remote(struct work_struct *work) WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3); curr->sched_class->task_tick(rq, curr, 0); + calc_load_nohz_remote(rq); out_unlock: rq_unlock_irq(rq, &rf); - out_requeue: + /* * Run the remote tick once per second (1Hz). This arbitrary * frequency is large enough to avoid overload but short enough diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c index 28a516575c18..de22da666ac7 100644 --- a/kernel/sched/loadavg.c +++ b/kernel/sched/loadavg.c @@ -231,16 +231,11 @@ static inline int calc_load_read_idx(void) return calc_load_idx & 1; } -void calc_load_nohz_start(void) +static void calc_load_nohz_fold(struct rq *rq) { - struct rq *this_rq = this_rq(); long delta; - /* - * We're going into NO_HZ mode, if there's any pending delta, fold it - * into the pending NO_HZ delta. - */ - delta = calc_load_fold_active(this_rq, 0); + delta = calc_load_fold_active(rq, 0); if (delta) { int idx = calc_load_write_idx(); @@ -248,6 +243,24 @@ void calc_load_nohz_start(void) } } +void calc_load_nohz_start(void) +{ + /* + * We're going into NO_HZ mode, if there's any pending delta, fold it + * into the pending NO_HZ delta. + */ + calc_load_nohz_fold(this_rq()); +} + +/* + * Keep track of the load for NOHZ_FULL, must be called between + * calc_load_nohz_{start,stop}(). + */ +void calc_load_nohz_remote(struct rq *rq) +{ + calc_load_nohz_fold(rq); +} + void calc_load_nohz_stop(void) { struct rq *this_rq = this_rq(); @@ -268,7 +281,7 @@ void calc_load_nohz_stop(void) this_rq->calc_load_update += LOAD_FREQ; } -static long calc_load_nohz_fold(void) +static long calc_load_nohz_read(void) { int idx = calc_load_read_idx(); long delta = 0; @@ -323,7 +336,7 @@ static void calc_global_nohz(void) } #else /* !CONFIG_NO_HZ_COMMON */ -static inline long calc_load_nohz_fold(void) { return 0; } +static inline long calc_load_nohz_read(void) { return 0; } static inline void calc_global_nohz(void) { } #endif /* CONFIG_NO_HZ_COMMON */ @@ -346,7 +359,7 @@ void calc_global_load(unsigned long ticks) /* * Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs. */ - delta = calc_load_nohz_fold(); + delta = calc_load_nohz_read(); if (delta) atomic_long_add(delta, &calc_load_tasks);
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