Messages in this thread Patch in this message | | | Date | Tue, 31 Jan 2023 10:35:19 +0800 | Subject | Re: [External] Re: [PATCH] sched/core: Avoid WARN_DOUBLE_CLOCK warning when CONFIG_SCHED_CORE | From | Hao Jia <> |
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On 2023/1/16 Peter Zijlstra wrote: > On Tue, Dec 06, 2022 at 03:05:50PM +0800, Hao Jia wrote: >> When we need to call update_rq_clock() to update the rq clock of >> other CPUs on the same core, before that we need to clear RQCF_UPDATED >> of rq->clock_update_flags to avoid the WARN_DOUBLE_CLOCK warning. >> Because at this time the rq->clock_update_flags of other CPUs >> may be RQCF_UPDATED. > > So you've found that the WARN_DOUBLE_CLOCK machinery doesn't work for > core-sched -- but then instead of fixing that machinery, you put > band-aids on it :/ > > Hi, Peter Sorry for the late reply. I just finished my holiday.
I am trying to adapt WARN_DOUBLE_CLOCK machinery for core-sched.
If sched_core_enabled(), we will get a core wide rq->lock, so we can safely clear RQCF_UPDATED of rq->clock_update_flags of all CPUs on this core. This avoids a WARN_DOUBLE_CLOCK warning when we call update_rq_clock() to update the rq clock of other cpus on the same core.
We cannot clear rq->clock_update_flags of other cpus on the same core in rq_pin_lock(). Because in some functions, we will temporarily give up core wide rq->lock, and then use raw_spin_rq_lock() to obtain core wide rq->lock, such as newidle_balance() and _double_lock_balance().
Thanks, Hao
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diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e838feb6adc5..f279912e30b3 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -435,6 +435,21 @@ sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
#endif /* CONFIG_SCHED_CORE */
+static inline void sched_core_rq_clock_clear_update(struct rq *rq) +{ +#ifdef CONFIG_SCHED_DEBUG + const struct cpumask *smt_mask; + int i; + if (rq->core_enabled) { + smt_mask = cpu_smt_mask(rq->cpu); + for_each_cpu(i, smt_mask) { + if (rq->cpu != i) + cpu_rq(i)->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP); + } + } +#endif +} + /* * Serialization rules: * @@ -546,6 +561,7 @@ void raw_spin_rq_lock_nested(struct rq *rq, int subclass) if (likely(lock == __rq_lockp(rq))) { /* preempt_count *MUST* be > 1 */ preempt_enable_no_resched(); + sched_core_rq_clock_clear_update(rq); return; } raw_spin_unlock(lock);
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