From: "Rafael J. Wysocki" <rafael@kernel.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: ramesh.thomas@intel.com, Linux PM <linux-pm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Reinette Chatre <reinette.chatre@intel.com>,
Alex Shi <alex.shi@linaro.org>,
Ulf Hansson <ulf.hansson@linaro.org>
Subject: Re: [PATCH] PM / QoS: Fix device resume latency PM QoS
Date: Tue, 24 Oct 2017 13:23:23 +0200 [thread overview]
Message-ID: <CAJZ5v0imdah_V1ErJsAUgh=vmsS3wtRsoRtgLQwxonGLzQrT-A@mail.gmail.com> (raw)
In-Reply-To: <2465945.6cfLQGiipl@aspire.rjw.lan>
On Tue, Oct 24, 2017 at 10:49 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Tuesday, October 24, 2017 7:54:09 AM CEST Ramesh Thomas wrote:
>> On 2017-10-20 at 13:27:34 +0200, Rafael J. Wysocki wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> >
[cut]
>> > @@ -63,10 +60,14 @@ static bool default_suspend_ok(struct de
>> >
>> > spin_unlock_irqrestore(&dev->power.lock, flags);
>> >
>> > - if (constraint_ns < 0)
>> > + if (constraint_ns == 0)
>> > return false;
>> >
>> > - constraint_ns *= NSEC_PER_USEC;
>> > + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
>> > + constraint_ns = -1;
>> > + else
>> > + constraint_ns *= NSEC_PER_USEC;
>> > +
>> > /*
>> > * We can walk the children without any additional locking, because
>> > * they all have been suspended at this point and their
>> > @@ -76,14 +77,19 @@ static bool default_suspend_ok(struct de
>> > device_for_each_child(dev, &constraint_ns,
>> > dev_update_qos_constraint);
>> >
>> > - if (constraint_ns > 0) {
>> > - constraint_ns -= td->suspend_latency_ns +
>> > - td->resume_latency_ns;
>> > - if (constraint_ns == 0)
>> > - return false;
>> > + if (constraint_ns < 0) {
>> > + /* The children have no constraints. */
>> > + td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
>> > + td->cached_suspend_ok = true;
>> > + } else {
>> > + constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
>> > + if (constraint_ns > 0) {
>> > + td->effective_constraint_ns = constraint_ns;
>> > + td->cached_suspend_ok = true;
>> > + } else {
>> > + td->effective_constraint_ns = 0;
>>
>> Previously effective_constraint_ns was left as -1 if constraint_ns becomes 0
>> Not sure if this change is intentional.
>
> Yes, it is.
>
>> I think at dev_update_qos_constraint, this can cause to skip call to
>> dev_pm_qos_read_value.
>
> I need to double check that.
If constraint_ns becomes 0 (or less) here, power cannot be removed
from the device, because it would add an unacceptable latency.
Thus effective_constraint_ns has to be 0 for it to indicate that
situation. If it was left at -1, it would mean "no requirement", but
that wouldn't be correct.
Thanks,
Rafael
next prev parent reply other threads:[~2017-10-24 11:23 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-20 11:27 [PATCH] PM / QoS: Fix device resume latency PM QoS Rafael J. Wysocki
2017-10-20 22:04 ` Reinette Chatre
2017-10-23 5:12 ` Alex Shi
2017-10-24 5:54 ` Ramesh Thomas
2017-10-24 8:49 ` Rafael J. Wysocki
2017-10-24 11:23 ` Rafael J. Wysocki [this message]
2017-10-24 11:35 ` [PATCH v2] " Rafael J. Wysocki
2017-10-25 7:16 ` Ramesh Thomas
2017-10-26 2:00 ` Ramesh Thomas
2017-10-26 8:44 ` Rafael J. Wysocki
2017-10-25 7:27 ` [PATCH] " Ramesh Thomas
2017-10-25 16:28 ` Rafael J. Wysocki
2017-10-26 1:41 ` Ramesh Thomas
2017-10-25 20:06 ` Andy Shevchenko
2017-10-26 8:38 ` Rafael J. Wysocki
2017-10-27 18:52 ` Andy Shevchenko
2017-10-27 19:16 ` Rafael J. Wysocki
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