Messages in this thread | | | Date | Sun, 2 Jul 2023 22:07:50 -0400 | Subject | Re: [PATCH v3] sched/core: introduce sched_core_idle_cpu() | From | Joel Fernandes <> |
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On 6/29/2023 12:02 AM, Cruz Zhao wrote: > As core scheduling introduced, a new state of idle is defined as > force idle, running idle task but nr_running greater than zero. > > If a cpu is in force idle state, idle_cpu() will return zero. This > result makes sense in some scenarios, e.g., load balance, > showacpu when dumping, and judge the RCU boost kthread is starving. > > But this will cause error in other scenarios, e.g., tick_irq_exit(): > When force idle, rq->curr == rq->idle but rq->nr_running > 0, results > that idle_cpu() returns 0. In function tick_irq_exit(), if idle_cpu() > is 0, tick_nohz_irq_exit() will not be called, and ts->idle_active will > not become 1, which became 0 in tick_nohz_irq_enter(). > ts->idle_sleeptime won't update in function update_ts_time_stats(), if > ts->idle_active is 0, which should be 1. And this bug will result that > ts->idle_sleeptime is less than the actual value, and finally will > result that the idle time in /proc/stat is less than the actual value. > > To solve this problem, we introduce sched_core_idle_cpu(), which > returns 1 when force idle. We audit all users of idle_cpu(), and > change idle_cpu() into sched_core_idle_cpu() in function > tick_irq_exit().
Reviewed-by: Joel Fernandes <joel@joelfernandes.org>
- Joel
> > v2-->v3: Only replace idle_cpu() with sched_core_idle_cpu() in > function tick_irq_exit(). And modify the corresponding commit log. > > Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com> > Reviewed-by: Peter Zijlstra <peterz@infradead.org> > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> > Reviewed-by: Joel Fernandes <joel@joelfernandes.org> > Link: https://lore.kernel.org/lkml/1687631295-126383-1-git-send-email-CruzZhao@linux.alibaba.com > --- > include/linux/sched.h | 2 ++ > kernel/sched/core.c | 13 +++++++++++++ > kernel/softirq.c | 2 +- > 3 files changed, 16 insertions(+), 1 deletion(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index b09a83bfad8b..73e61c0f10a7 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2430,9 +2430,11 @@ extern void sched_core_free(struct task_struct *tsk); > extern void sched_core_fork(struct task_struct *p); > extern int sched_core_share_pid(unsigned int cmd, pid_t pid, enum pid_type type, > unsigned long uaddr); > +extern int sched_core_idle_cpu(int cpu); > #else > static inline void sched_core_free(struct task_struct *tsk) { } > static inline void sched_core_fork(struct task_struct *p) { } > +static inline int sched_core_idle_cpu(int cpu) { return idle_cpu(cpu); } > #endif > > extern void sched_set_stop_task(int cpu, struct task_struct *stop); > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 71c1a0f232b4..c80088956987 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7286,6 +7286,19 @@ struct task_struct *idle_task(int cpu) > return cpu_rq(cpu)->idle; > } > > +#ifdef CONFIG_SCHED_CORE > +int sched_core_idle_cpu(int cpu) > +{ > + struct rq *rq = cpu_rq(cpu); > + > + if (sched_core_enabled(rq) && rq->curr == rq->idle) > + return 1; > + > + return idle_cpu(cpu); > +} > + > +#endif > + > #ifdef CONFIG_SMP > /* > * This function computes an effective utilization for the given CPU, to be > diff --git a/kernel/softirq.c b/kernel/softirq.c > index c8a6913c067d..98b98991ce45 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -630,7 +630,7 @@ static inline void tick_irq_exit(void) > int cpu = smp_processor_id(); > > /* Make sure that timer wheel updates are propagated */ > - if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) { > + if ((sched_core_idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) { > if (!in_hardirq()) > tick_nohz_irq_exit(); > }
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