Re: [PATCH v2 2/4] PM / devfreq: cache the last call to get_dev_status()

[MyungJoo Ham <myungjoo.ham@samsung.com>]

> The return value of get_dev_status() can be reused.  Cache it so that
> other parts of the kernel can reuse it instead of having to call the
> same function again.
> 
> Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
> Cc: Kyungmin Park <kyungmin.park@samsung.com>
> Signed-off-by: Javi Merino <javi.merino@arm.com>
> ---
> 
> This patch tries to let multiple components.  To summarize the
> discussion in v1[1] I can think of three alternatives:
> 
>   1) Change get_dev_status() to return absolute values for busy_time
>      and total_time
>   2) Make core devfreq call get_dev_status() periodically (for
>      example, before calling the governor) and all the entities that
>      want access can do so via a pointer in devfreq
>   3) Make the simple ondemand governor call get_dev_status()
>      periodically and cache it, forcing all the other entities to
>      rely on that governor being active
> 
> [1] http://thread.gmane.org/gmane.linux.power-management.general/61936/focus=61993
> 
> This patch implements option 3)
> 
>  drivers/devfreq/devfreq.c                 |  5 +++++
>  drivers/devfreq/governor_simpleondemand.c | 33 +++++++++++++++++--------------
>  include/linux/devfreq.h                   |  7 +++++++
>  3 files changed, 30 insertions(+), 15 deletions(-)
> 

Dear Javi,


Another question has risen as seeing Chanwoo's RFC patches,
which have a similar objective to different devices with
much less intervention:

[RFC PATCH 0/2] thermal: Add generic devfreq cooling device
https://lkml.org/lkml/2015/7/16/334
(This patch set also requires updates as it appears not
to use opp notifiers properly, but it shows the direction
on how to implement thermal/qos inputs to devfreq devices)

Can't you simply use OPP's disable/enable functions and
let devfreq automatically update itself accordingly?
It simplifies your codes as well especially if you put
your possible frequencies to DT.


Cheers,
MyungJoo

ps. Chanwoo, I will comment on your patches on the usage of
opp-notifiers as well.