From: Lukasz Luba <lukasz.luba@arm.com>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
amitk@kernel.org, rui.zhang@intel.com
Subject: Re: [PATCH 1/2] thermal: power_allocator: maintain the device statistics from going stale
Date: Tue, 6 Apr 2021 09:44:02 +0100 [thread overview]
Message-ID: <1f0710d5-cd78-dfff-1ce2-bba5f6e469b7@arm.com> (raw)
In-Reply-To: <b27e0c79-de27-f9b1-ad16-17825b302615@linaro.org>
On 4/2/21 4:54 PM, Daniel Lezcano wrote:
> On 31/03/2021 18:33, Lukasz Luba wrote:
>> When the temperature is below the first activation trip point the cooling
>> devices are not checked, so they cannot maintain fresh statistics. It
>> leads into the situation, when temperature crosses first trip point, the
>> statistics are stale and show state for very long period.
>
> Can you elaborate the statistics you are referring to ?
>
> I can understand the pid controller needs temperature but I don't
> understand the statistics with the cooling device.
>
>
The allocate_power() calls cooling_ops->get_requested_power(),
which is for CPUs cpufreq_get_requested_power() function.
In that cpufreq implementation for !SMP we still has the
issue of stale statistics. Viresh, when he introduced the usage
of sched_cpu_util(), he fixed that 'long non-meaningful period'
of the broken statistics and it can be found since v5.12-rc1.
The bug is still there for the !SMP. Look at the way how idle time
is calculated in get_load() [1]. It relies on 'idle_time->timestamp'
for calculating the period. But when this function is not called,
the value can be very far away in time, e.g. a few seconds back,
when the last allocate_power() was called.
The bug is there for both SMP and !SMP [2] for older kernels, which can
be used in Android or ChromeOS. I've been considering to put this simple
IPA fix also to some other kernels, because Viresh's change is more
a 'feature' and does not cover both platforms.
Regards,
Lukasz
[1]
https://elixir.bootlin.com/linux/v5.12-rc5/source/drivers/thermal/cpufreq_cooling.c#L156
[2]
https://elixir.bootlin.com/linux/v5.11.11/source/drivers/thermal/cpufreq_cooling.c#L143
next prev parent reply other threads:[~2021-04-06 8:44 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 16:33 [PATCH 0/2] Improve IPA mechanisms in low temperature state Lukasz Luba
2021-03-31 16:33 ` [PATCH 1/2] thermal: power_allocator: maintain the device statistics from going stale Lukasz Luba
2021-04-02 15:54 ` Daniel Lezcano
2021-04-06 8:44 ` Lukasz Luba [this message]
2021-04-06 10:16 ` Daniel Lezcano
2021-04-06 10:39 ` Lukasz Luba
2021-04-06 11:24 ` Daniel Lezcano
2021-04-06 12:25 ` Lukasz Luba
2021-04-06 14:32 ` Daniel Lezcano
2021-04-06 18:38 ` Lukasz Luba
2021-04-06 19:45 ` Daniel Lezcano
2021-03-31 16:33 ` [PATCH 2/2] thermal: power_allocator: update once cooling devices when temp is low Lukasz Luba
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1f0710d5-cd78-dfff-1ce2-bba5f6e469b7@arm.com \
--to=lukasz.luba@arm.com \
--cc=amitk@kernel.org \
--cc=daniel.lezcano@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=rui.zhang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).