Re: [PATCH V2 06/20] blk-mq-sched: don't dequeue request until all in ->dispatch are flushed

[Bart Van Assche <Bart.VanAssche@xxxxxxx>]

On Sat, 2017-08-05 at 14:56 +0800, Ming Lei wrote:
> +	/*
> +	 * Wherever DISPATCH_BUSY is set, blk_mq_run_hw_queue()
> +	 * will be run to try to make progress, so it is always
> +	 * safe to check the state here.
> +	 */
> +	if (test_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state))
> +		return;

The comment above test_bit() is useful but does not explain the purpose of
the early return. Is the purpose of the early return perhaps to serialize
blk_mq_sched_dispatch_requests() calls? If so, please mention this.

Thanks,

Bart.