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

[Bart Van Assche <Bart.VanAssche@wdc.com>]

On Fri, 2018-08-10 at 09:51 +0800, jianchao.wang wrote:
> 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 au=
tosuspend_delay_ms
> > +	 * ago. Since blk_queue_enter() is called by the=
 request allocation
> > +	 * code before pm_request_resume(), if no reques=
ts 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_q=
ueue_enter()
> > +		 * calls see the preempt-only state. See also
> > +		 *=20
> > https://urldefense.proofpoint.com/v2/url?u=http-3A__l=
wn.net_Articles_573497_&d=DwIBAg&c=RoP1YumCXCgaWH=
vlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26A=
Tvfo6QSTvZyQ&m=U9uPCJD2WnkXvdzrWaKPh2wJuk8-IHvxZ9sWDVrg2Tg&s=
0-c9E23TPCpNQkiZpuzGztwHxjWF8qrESfRnPmI-e-Z48&e=
> > .
> > +		 */
> > +		synchronize_rcu();
> > +		if (blk_requests_in_flight(q) == 0)
> > +			ret = 0;
> > +	}
>=20
> I still think blk_set_pm_only should be moved after blk=
F8-requests_in_flight.
> Otherwise, the normal IO will be blocked for a little while if there =
are still
> busy requests.

Hi Jianchao,

Although I think it is unlikely that the scenario you described will happen=
, I
will make the change you requested.

Bart.