linux-kernel - Re: [PATCH v4] sched/core: Adapt WARN_DOUBLE

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Date:   Thu, 4 May 2023 09:23:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hao Jia <jiahao.os@...edance.com>
Cc:     mingo@...hat.com, mingo@...nel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
        Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v4] sched/core: Adapt WARN_DOUBLE_CLOCK machinery for
 core-sched

On Thu, Apr 06, 2023 at 02:44:15PM +0800, Hao Jia wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0d18c3969f90..c6e2c79152ef 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -429,11 +429,32 @@ void sched_core_put(void)
>  		schedule_work(&_work);
>  }
>  
> +/*
> + * Now, we have obtained a core-wide rq->lock, then we need to clear
> + * RQCF_UPDATED of rq->clock_update_flags of the sibiling CPU
> + * on this core to avoid the WARN_DOUBLE_CLOCK warning.
> + */
> +static inline void sched_core_clear_rqcf_updated(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
> +}
>  #else /* !CONFIG_SCHED_CORE */
>  
>  static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
>  static inline void
>  sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
> +static inline void sched_core_clear_rqcf_updated(struct rq *rq) { }
>  
>  #endif /* CONFIG_SCHED_CORE */
>  
> @@ -548,6 +569,7 @@ 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_clear_rqcf_updated(rq);
>  			return;
>  		}
>  		raw_spin_unlock(lock);

This still looks absolutely wrong. The whole RQCF thing is a pin action.