Re: [PATCH v6 11/12] block: Change the runtime power management approach (2/2)

["jianchao.wang" <jianchao.w.wang@oracle.com>]

Hi Bart

On 08/10/2018 03:41 AM, Bart Van Assche wrote:
> +
> +	blk_set_pm_only(q);
> +	/*
> +	 * This function only gets called if the most recent
> +	 * pm_request_resume() call occurred at least autosuspend_delay_ms
> +	 * ago. Since blk_queue_enter() is called by the request allocation
> +	 * code before pm_request_resume(), if no requests have a tag assigned
> +	 * it is safe to suspend the device.
> +	 */
> +	ret = -EBUSY;
> +	if (blk_requests_in_flight(q) == 0) {
> +		/*
> +		 * Call synchronize_rcu() such that later blk_queue_enter()
> +		 * calls see the preempt-only state. See also
> +		 * https://urldefense.proofpoint.com/v2/url?u=http-3A__lwn.net_Articles_573497_&d=DwIBAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26ATvfo6QSTvZyQ&m=U9uPCJD2WnkXvdzrWaKPh2wJuk8-IHvxZ9sWDVrg2Tg&s=c9E23TPCpNQkiZpuzGztwHxjWF8qrESfRnPmI-e-Z48&e=.
> +		 */
> +		synchronize_rcu();
> +		if (blk_requests_in_flight(q) == 0)
> +			ret = 0;
> +	}

I still think blk_set_pm_only should be moved after blk_requests_in_flight.
Otherwise, the normal IO will be blocked for a little while if there are still
busy requests.

Thanks
Jianchao