Re: [PATCH v2] blk-mq: use a housekeeping CPU for passthrough requests on isolated hctxs

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-11-03 15:57:22 [+0100], Daniel Wagner wrote:
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -717,6 +717,25 @@ struct request *blk_mq_alloc_request(struct request_queue *q, blk_opf_t opf,
>  }
>  EXPORT_SYMBOL(blk_mq_alloc_request);
>  
> +/*
> + * Return an online CPU which is neither isolated from the scheduler domains
> + * nor from managed interrupts, or nr_cpu_ids if there is none.
> + */
> +static unsigned int blk_mq_housekeeping_cpu(void)
> +{
> +	unsigned int cpu;
> +
> +	rcu_read_lock();
> +	for_each_online_cpu(cpu) {
> +		if (!cpu_is_isolated(cpu) &&
> +		    housekeeping_test_cpu(cpu, HK_TYPE_MANAGED_IRQ))
> +			break;
> +	}

What about
	guard(rcu);
	for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)) {
		if (!cpu_is_isolated(cpu)
			break;
	}

this ends up with one less function call ;)

> +	rcu_read_unlock();
> +
> +	return cpu;
> +}
> +
>  struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>  	blk_opf_t opf, blk_mq_req_flags_t flags, unsigned int hctx_idx)
>  {

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian