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From: Viresh Kumar <viresh.kumar@linaro.org>
To: Saravana Kannan <saravanak@google.com>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Android Kernel Team <kernel-team@android.com>,
	Linux PM <linux-pm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 0/3] Add required-opps support to devfreq passive gov
Date: Wed, 26 Jun 2019 12:02:40 +0530
Message-ID: <20190626063240.kgdiy7xsz4mahrdr@vireshk-i7> (raw)
In-Reply-To: <CAGETcx_v05PfscMi2qiYwHRMLryyA_494+h+kmJ3mD+GOjjeLA@mail.gmail.com>

On 24-06-19, 22:29, Saravana Kannan wrote:
> No, the CPUs will be the "parent" and the cache will be the "child".
> CPU is a special case when it comes to the actual software (not DT) as
> we'll need the devfreq governor to look at all the CPUfreq policies to
> decide the cache frequency (max of all their requirements).
> 
> I think "master" and "slave" would have been a better term as the
> master device determines its frequency using whatever means and the
> "slave" device just "follows" the master device.

Okay, so to confirm again this is what we will have:

- CPUs are called masters and Caches are slaves.

- The devfreq governor we are talking about takes care of changing
  frequency of caches (slaves) and chooses a target frequency for
  caches based on what the masters are running at.

- The CPUs OPP nodes will have required-opps property and will be
  pointing to the caches OPP nodes. The CPUs may already be using
  required-opps node for PM domain performance state thing.


Now the problem is "required-opp" means something really *required*
and it is not optional. Like a specific voltage level before we can
switch to a particular frequency. And this is how I have though of it
until now. And this shouldn't be handled asynchronously, i.e. required
OPPs must be set while configuring OPP of a device.

So, when a CPU changes frequency, we must change the performance state
of PM domain and change frequency/bw of the cache synchronously. And
in such a case "required-opps" can be a very good fit for this use
case.

But with what you are trying to do it is no longer required-opp but
good-to-have-opp. And that worries me.

-- 
viresh

  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-22  0:34 Saravana Kannan
2019-06-22  0:34 ` [PATCH v1 1/3] OPP: Allow required-opps even if the device doesn't have power-domains Saravana Kannan
2019-06-22  0:34 ` [PATCH v1 2/3] OPP: Add function to look up required OPP's for a given OPP Saravana Kannan
2019-06-22 11:49   ` Chanwoo Choi
2019-06-22 21:41     ` Saravana Kannan
2019-06-23  4:27       ` Chanwoo Choi
2019-06-23  6:07         ` Saravana Kannan
2019-06-22  0:34 ` [PATCH v1 3/3] PM / devfreq: Add required OPPs support to passive governor Saravana Kannan
2019-06-22 12:00   ` Chanwoo Choi
2019-06-22 21:45     ` Saravana Kannan
2019-06-24  9:43 ` [PATCH v1 0/3] Add required-opps support to devfreq passive gov Viresh Kumar
2019-06-24 22:17   ` Saravana Kannan
2019-06-25  4:10     ` Viresh Kumar
2019-06-25  5:00       ` Saravana Kannan
2019-06-25  5:22         ` Viresh Kumar
2019-06-25  5:29           ` Saravana Kannan
2019-06-26  6:32             ` Viresh Kumar [this message]
2019-06-26 18:10               ` Saravana Kannan
2019-06-28  6:49                 ` Viresh Kumar
2019-06-28 20:26                   ` Saravana Kannan
2019-07-11 23:16                     ` Saravana Kannan

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