Re: [PATCH 2/7] sched/core: Simplify/fix time updates

[Tejun Heo]

Hello,

On Fri, Aug 28, 2026 at 12:17:01PM +0200, Peter Zijlstra wrote:
> +static void opt_update_rq_clock(struct rq *rq)
> +{
> +	if (!(rq->clock_update_flags & RQCF_UPDATED))
> +		update_rq_clock(rq);
> +}

Yeah, I think this really needs sth like this. That said,

> @@ -6336,18 +6336,12 @@ pick_next_task(struct rq *rq, struct rq_
>  		 * pick_next_task(). If the current cpu is not the core,
>  		 * the core may also have been updated above.
>  		 */
> -		if (i != cpu && (rq_i != rq->core || !core_clock_updated))
> -			update_rq_clock(rq_i);
> +		opt_update_rq_clock(rq_i);

I don't think this is correct. A sibling rq wouldn't necessarily have
RCQF_UPDATED cleared from whenever it scheduled / ticked the last time, so
the following pick_task() can run with pretty stale rq clock.

>  
> -		p = pick_task(rq_i, rf);
> +		p = pick_task(rq_i, &rf_i);
>  		if (unlikely(seq != rq->core->core_task_seq ||
> -			     WARN_ON_ONCE(p == RETRY_TASK))) {
> -			/* rq lock may have been dropped, clocks invalidated */
> -			core_clock_updated = false;
> -			if (!(rq->clock_update_flags & RQCF_UPDATED))
> -				update_rq_clock(rq);
> +			     WARN_ON_ONCE(p == RETRY_TASK)))
>  			goto restart;
> -		}

Thanks.

-- 
tejun