linux-kernel - Re: [PATCH v3 0/7] drivers: devfreq: fix and optimize workqueue mechanism

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Message-ID: <d9245497-ec63-4a5d-6c00-0ec2954af735@samsung.com>
Date:   Wed, 13 Feb 2019 09:18:21 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Lukasz Luba <l.luba@...tner.samsung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     b.zolnierkie@...sung.com, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, m.szyprowski@...sung.com,
        s.nawrocki@...sung.com, joel@...lfernandes.org,
        chris.diamand@....com, mka@...omium.org, rostedt@...dmis.org,
        mingo@...hat.com
Subject: Re: [PATCH v3 0/7] drivers: devfreq: fix and optimize workqueue
 mechanism

On 19. 2. 13. 오전 7:23, Lukasz Luba wrote:
> This patch set changes workqueue related features in devfreq framework.
> First patch switches to delayed work instead of deferred.
> The second switches to regular system work and deletes custom 'devfreq'.
> 
> Using deferred work in this context might harm the system performance.
> When the CPU enters idle, deferred work is not fired. The devfreq device's
> utilization does not have to be connected with a particular CPU.
> The drivers for GPUs, Network on Chip, cache L3 rely on devfreq governor.
> They all are missing opportunity to check the HW state and react when
> the deferred work is not fired.
> A corner test case, when Dynamic Memory Controller is utilized by CPUs running
> on full speed, might show x5 worse performance if the crucial CPU is in idle.
> 
> There was a discussion regarding v2 that the power usage because of waking up

We have not yet finished the any discussion. We only just had a few reply
and you didn't wait for any reply from other. As I already commented
on exynos5422-dmc series, please don't send the next patch
without any final agreement.

In this series, patch1/patch2 are same at version 2 patchset.
Even if we need to discuss more them, you just send same patches
without any agreement among reviewers. At least, you have to wait the reply
instead of just sending the new patchset. It is basic review rule on mailing list.


> an idle CPU would be too high. In my opinion it won't and fixing bug is more
> important than < 1% more power used [1].
> I have addressed also this issue. In this patch set there is a mechanism
> which prevents from to frequent checks when there is no need.
> When the device enters its lowest state (OPP) the framework sets polling
> interval to 'polling_idle_ms'. In default Kconfig it is 500ms, so 2 times per
> second.
> It is tunable from the sysfs interface per device, thus driver developer can
> experiment and choose best intervals for the system.
> 
> Changes:
> v3:
> - reordered first two patches
> - added functionality to lower power consumption when the device is less busy;
>   there is a new polling interval enabled when device enters lowest frequency;
> - added trace events to capture the behaviour of the system
> v2:
> - single patch split into two
> - added cover letter
> 
> link for the previous version and discussion:
> https://marc.info/?l=linux-pm&m=154989907416072&w=2
> https://marc.info/?l=linux-pm&m=154904631226997&w=2
> 
> Regards,
> Lukasz Luba
> 
> [1] https://marc.info/?l=linux-kernel&m=155000641622443&w=2
> 
> Lukasz Luba (7):
>   drivers: devfreq: change deferred work into delayed
>   drivers: devfreq: change devfreq workqueue mechanism
>   Kconfig: drivers: devfreq: add default idle polling
>   include: devfreq: add polling_idle_ms to 'profile'
>   drivers: devfreq: add longer polling interval in idle
>   trace: events: add devfreq trace event file
>   drivers: devfreq: add tracing for scheduling work
> 
>  MAINTAINERS                               |   1 +
>  drivers/devfreq/Kconfig                   |  13 +++
>  drivers/devfreq/devfreq.c                 | 184 ++++++++++++++++++++++++------
>  drivers/devfreq/governor.h                |   3 +-
>  drivers/devfreq/governor_simpleondemand.c |   6 +-
>  include/linux/devfreq.h                   |   6 +
>  include/trace/events/devfreq.h            |  39 +++++++
>  7 files changed, 218 insertions(+), 34 deletions(-)
>  create mode 100644 include/trace/events/devfreq.h
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics