Messages in this thread | | | From | Joel Fernandes <> | Date | Tue, 4 Jul 2023 09:19:32 -0400 | Subject | Re: [PATCH v3] sched/core: introduce sched_core_idle_cpu() |
| |
On Tue, Jul 4, 2023 at 1:40 AM Aaron Lu <aaron.lu@intel.com> wrote: > > On Thu, Jun 29, 2023 at 12:02:04PM +0800, 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(). > > > > 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; > > If the intention is to consider forced idle cpus as idle, then should > the above condition written as: > > if (sched_core_enabled(rq) && rq->core->core_forceidle_count) > return 1; > ? > > Or as long as a single cookied task is running, all normal idle cpus are > regarded forced idle here and 1 is returned while previously, idle_cpu() > is called for those cpus and if they have wakeup task pending, they are > not regarded as idle so looks like a behaviour change. >
Ah you're right, great insight. _sigh_ I should not have missed that during review. It will change idle_cpu() behavior if core sched is enabled...
- Joel
| |