On Mon, Jul 27, 2020 at 03:05:40PM -0600, Jens Axboe wrote:
> +void blk_mq_quiesce_queue_wait(struct request_queue *q)
> {
> struct blk_mq_hw_ctx *hctx;
> unsigned int i;
> bool rcu = false;
>
> - blk_mq_quiesce_queue_nowait(q);
> -
> queue_for_each_hw_ctx(q, hctx, i) {
> if (hctx->flags & BLK_MQ_F_BLOCKING)
> synchronize_srcu(hctx->srcu);
> else
> rcu = true;
> }
> +
> if (rcu)
> synchronize_rcu();
> }
Either all the hctx's are blocking or none of them are: we don't need to
iterate the hctx's to see which sync method to use. We can add at the
very beginning (and get rid of 'bool rcu'):
if (!(q->tag_set->flags & BLK_MQ_F_BLOCKING)) {
synchronize_rcu();
return;
}
But the issue Sagi is trying to address is quiescing a lot
request queues sharing a tagset where synchronize_rcu() is too time
consuming to do repeatedly. He wants to synchrnoize once for the entire
tagset rather than per-request_queue, so I think he needs an API taking
a 'struct blk_mq_tag_set' instead of a 'struct request_queue'.
