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

jianchao.wang
2018-08-10T01:51:12Z

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