Linux-PM Archive on
 help / color / Atom feed
From: Lukasz Luba <>
Subject: Re: [PATCH 0/1] drivers: devfreq: use DELAYED_WORK in DEVFREQ monitoring subsystem
Date: Thu, 30 Jan 2020 11:47:57 +0000
Message-ID: <> (raw)
In-Reply-To: <>

Hi Chanwoo, MyungJoo,

Gentle ping. The issue is not only in the devfreq itself,
but also it affects thermal. The devfreq cooling rely on
busy_time and total_time updated by the devfreq monitoring
(in simple_ondemand).
Thermal uses DELAYED_WORK and is more reliable, but uses stale
data from devfreq_dev_stats. It is especially visible when
you have cgroup spanning one cluster. Android uses cgroups
heavily. You can make easily this setup using 'taskset',
run some benchmarks and observe 'devfreq_monitor' traces and
timestamps, i.e. for your exynos-bus.

The patch is really non-invasive and simple. It can be a good starting
point for testing and proposing other solutions.


On 1/27/20 3:17 PM, wrote:
> From: Lukasz Luba <>
> Hi all,
> This patch is a continuation of my previous work for fixing DEVFREQ monitoring
> subsystem [1]. The issue is around DEFERRABLE_WORK, which uses TIMER_DEFERRABLE
> under the hood which will work normally when the system is busy, but will not
> cause a CPU to come out of idle and serve the DEVFREQ monitoring requests.
> This is especially important in the SMP systems with many CPUs, when the load
> balance tries to keep some CPUs idle. The next service request could not be
> triggered when the CPU went idle in the meantime.
> The DELAYED_WORK is going to be triggered even on an idle CPU. This will allow
> to call the DEVFREQ monitoring in reliable intervals. Some of the drivers might
> use internal counters to monitor their load, when the DEVFREQ work is not
> triggered in a predictable way, these counters might overflow leaving the
> device in undefined state.
> To observe the difference, the trace output might be used, i.e.
> echo 1 > /sys/kernel/debug/tracing/events/devfreq/enable
> #your test starts here, i.e. 'sleep 5' or 'dd ' or 'gfxbench'
> echo 0 > /sys/kernel/debug/tracing/events/devfreq/enable
> cat /sys/kernel/debug/tracing/trace
> When there are some registered devfreq drivers, you should see the traces
> 'devfreq_moniotor' triggered in reliable intervals.
> The patch set is based on Chanwoo's devfreq repository and branch
> 'devfreq-next' [2].
> Regards,
> Lukasz Luba
> [1]
> [2]
> Lukasz Luba (1):
>    drivers: devfreq: add DELAYED_WORK to monitoring subsystem
>   drivers/devfreq/Kconfig   | 19 +++++++++++++++++++
>   drivers/devfreq/devfreq.c |  6 +++++-
>   2 files changed, 24 insertions(+), 1 deletion(-)

      parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-27 15:17 lukasz.luba
2020-01-27 15:17 ` [PATCH 1/1] drivers: devfreq: add DELAYED_WORK to " lukasz.luba
2020-01-30 11:47 ` [PATCH 0/1] drivers: devfreq: use DELAYED_WORK in DEVFREQ " Lukasz Luba
2020-01-31  0:42   ` Chanwoo Choi
2020-01-31  0:47     ` Chanwoo Choi
2020-01-31  9:38       ` Lukasz Luba
2020-02-03  1:10         ` Chanwoo Choi
2020-01-30 11:47 ` Lukasz Luba [this message]

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:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-PM Archive on

Archives are clonable:
	git clone --mirror linux-pm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-pm linux-pm/ \
	public-inbox-index linux-pm

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone