From: Ulf Hansson <ulf.hansson@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux PM <linux-pm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Tero Kristo <t-kristo@ti.com>,
Reinette Chatre <reinette.chatre@intel.com>,
Ramesh Thomas <ramesh.thomas@intel.com>,
Alex Shi <alex.shi@linaro.org>
Subject: Re: [RFT][PATCH v2 1/2] PM / domains: Rework governor code to be more consistent
Date: Mon, 6 Nov 2017 13:44:37 +0100 [thread overview]
Message-ID: <CAPDyKFpCZov7nJVijToJ7k_YJb_CKAeScpRC5KhrZ8qdiDFSVg@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0jmeqxZyws_hS8T8pZdHK2p3kzzAA4-jaJw9+v9gv1DRQ@mail.gmail.com>
[...]
>>> static int dev_update_qos_constraint(struct device *dev, void *data)
>>> {
>>> s64 *constraint_ns_p = data;
>>> - s32 constraint_ns = -1;
>>> -
>>> - if (dev->power.subsys_data && dev->power.subsys_data->domain_data)
>>> - constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
>>> + s64 constraint_ns;
>>>
>>> - if (constraint_ns < 0) {
>>> - constraint_ns = dev_pm_qos_read_value(dev);
>>> - constraint_ns *= NSEC_PER_USEC;
>>> - }
>>> - if (constraint_ns == 0)
>>> + if (!dev->power.subsys_data || !dev->power.subsys_data->domain_data)
>>> return 0;
>>>
>>> /*
>>> - * constraint_ns cannot be negative here, because the device has been
>>> - * suspended.
>>> + * Only take suspend-time QoS constraints of devices into account,
>>> + * because constraints updated after the device has been suspended are
>>> + * not guaranteed to be taken into account anyway. In order for them
>>> + * to take effect, the device has to be resumed and suspended again.
>>> */
>>
>> This means a change in behavior, because earlier we took into account
>> QoS values for child devices that were not attached to a genpd.
>
> OK
>
> I have overlooked it or rather have forgotten about that.
>
>> Is there any reason you think we should change this, or is it just
>> something you overlooked here?
>>
>> I understand, that if the QoS constraint has been updated after such
>> child device has been suspended, it's tricky to take a correct
>> decision.
>
> Right, but if they are not in a domain, the best we can do is to look
> at the current value.
>
>> To really solve this, we would either have to register a QoS notifier
>> for all children devices that has its parent attached to a genpd, or
>> always runtime resume devices before updating QoS constraints.
>>
>> Non of these options is perfect, so perhaps we should consider a "best
>> effort" approach instead? Whatever that may be.
>
> I think best effort makes most sense.
Okay!
>
> So I guess I'll simply evaluate dev_pm_qos_read_value(dev) if
> subsys_data or subsys_data->domain_data is not there.
Yes.
However, if it returns -1, what value should you pick? 0?
>
> Of course, that doesn't apply to the code in __default_power_down_ok()
> as that only takes device in the domain into account anyway.
Yep, agree!
Kind regards
Uffe
next prev parent reply other threads:[~2017-11-06 12:44 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-01 23:00 [RFT][PATCH 0/2] PM / QoS: Device resume latency framework fix Rafael J. Wysocki
2017-11-01 23:01 ` [RFT][PATCH 1/2] PM / domains: Rework governor code to be more consistent Rafael J. Wysocki
2017-11-03 7:05 ` Ramesh Thomas
2017-11-03 7:51 ` Rafael J. Wysocki
2017-11-01 23:03 ` [RFT][PATCH 2/2] PM / QoS: Fix device resume latency framework Rafael J. Wysocki
2017-11-03 7:43 ` Ramesh Thomas
2017-11-03 7:58 ` Rafael J. Wysocki
2017-11-03 10:38 ` Rafael J. Wysocki
2017-11-03 11:42 ` [RFT][PATCH v2 0/2] PM / QoS: Device resume latency framework fix Rafael J. Wysocki
2017-11-03 11:47 ` [RFT][PATCH v2 1/2] PM / domains: Rework governor code to be more consistent Rafael J. Wysocki
2017-11-04 2:34 ` Ramesh Thomas
2017-11-04 11:24 ` Rafael J. Wysocki
2017-11-06 7:47 ` Ramesh Thomas
2017-11-06 12:10 ` Ulf Hansson
2017-11-06 12:34 ` Rafael J. Wysocki
2017-11-06 12:44 ` Ulf Hansson [this message]
2017-11-06 12:49 ` Rafael J. Wysocki
2017-11-06 14:38 ` Ulf Hansson
2017-11-06 23:07 ` Rafael J. Wysocki
2017-11-03 11:50 ` [RFT][PATCH v2 2/2] PM / QoS: Fix device resume latency framework Rafael J. Wysocki
2017-11-03 16:39 ` Reinette Chatre
2017-11-04 2:28 ` Ramesh Thomas
2017-11-04 11:30 ` Rafael J. Wysocki
2017-11-04 11:58 ` Rafael J. Wysocki
2017-11-04 11:28 ` Rafael J. Wysocki
2017-11-04 2:38 ` Ramesh Thomas
2017-11-04 12:34 ` [RFT][Update][PATCH " Rafael J. Wysocki
2017-11-06 17:47 ` Reinette Chatre
2017-11-07 1:07 ` Rafael J. Wysocki
2017-11-06 13:46 ` [RFT][PATCH v2 0/2] PM / QoS: Device resume latency framework fix Geert Uytterhoeven
2017-11-07 1:08 ` Rafael J. Wysocki
2017-11-08 9:09 ` Tero Kristo
2017-11-07 1:17 ` [PATCH v3 " Rafael J. Wysocki
2017-11-07 1:23 ` [PATCH v3 1/2] PM / domains: Rework governor code to be more consistent Rafael J. Wysocki
2017-11-07 5:05 ` Ramesh Thomas
2017-11-07 10:22 ` Rafael J. Wysocki
2017-11-07 23:24 ` Ramesh Thomas
2017-11-10 7:49 ` Ulf Hansson
2017-11-07 1:27 ` [PATCH v3 2/2] PM / QoS: Fix device resume latency framework Rafael J. Wysocki
2017-11-07 4:33 ` Ramesh Thomas
2017-11-07 10:12 ` Rafael J. Wysocki
2017-11-07 10:33 ` [PATCH v4 " Rafael J. Wysocki
2017-11-07 23:15 ` Ramesh Thomas
2017-11-08 0:09 ` Rafael J. Wysocki
2017-11-10 7:49 ` Ulf Hansson
2017-11-10 8:03 ` Geert Uytterhoeven
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