Linux-PM Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH 0/1] drivers: devfreq: use DELAYED_WORK in DEVFREQ monitoring subsystem
@ 2020-01-27 15:17 lukasz.luba
  2020-01-27 15:17 ` [PATCH 1/1] drivers: devfreq: add DELAYED_WORK to " lukasz.luba
                   ` (2 more replies)
  0 siblings, 3 replies; 8+ messages in thread
From: lukasz.luba @ 2020-01-27 15:17 UTC (permalink / raw)
  To: myungjoo.ham, kyungmin.park, cw00.choi, linux-pm, linux-kernel
  Cc: b.zolnierkie, lukasz.luba

From: Lukasz Luba <lukasz.luba@arm.com>

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] https://lkml.org/lkml/2019/2/12/1179
[2] https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/log/?h=devfreq-next


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(-)

-- 
2.17.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, back to index

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-27 15:17 [PATCH 0/1] drivers: devfreq: use DELAYED_WORK in DEVFREQ monitoring subsystem 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

Linux-PM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-pm/0 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/ https://lore.kernel.org/linux-pm \
		linux-pm@vger.kernel.org
	public-inbox-index linux-pm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git