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From: Matthias Kaehlcke <mka@chromium.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Leonard Crestez <leonard.crestez@nxp.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Saravana Kannan <saravanak@google.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] cpufreq: Add user_min/max_freq
Date: Thu, 31 Oct 2019 15:23:56 -0700	[thread overview]
Message-ID: <20191031222356.GE27773@google.com> (raw)
In-Reply-To: <3169109.BFaCN5124U@kreacher>

On Thu, Oct 31, 2019 at 11:24:31AM +0100, Rafael J. Wysocki wrote:
> On Wednesday, October 30, 2019 1:41:49 AM CET Leonard Crestez wrote:
> > Current values in scaling_min_freq and scaling_max freq can change on
> > the fly due to event such as thermal monitoring.
> 
> Which is intentional.
> 
> > This behavior is confusing for userspace and because once an userspace
> > limit is written to scaling_min/max_freq it is not possible to read it back.
> 
> That can be argued both ways.
> 
> It is also useful to know the effective constraints and arguably the ability
> to read back the values that you have written is mostly needed for debugging
> the code.

Agreed that reading the values back is probably mostly useful for debugging.

Reading the effective constraints is a debugging use case as well, userspace
can't make any decisions based on values which might be in constant flux.

IMO the current interface is completely counterintuitive, I really hope we
wouldn't implement it the same way if given a chance to do it again. If there
is use for reading the effective constraints it should be exposed as a separate
read-only attribute. Keep it simple (when possible).

WARNING: multiple messages have this Message-ID (diff)
From: Matthias Kaehlcke <mka@chromium.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
	Saravana Kannan <saravanak@google.com>,
	linux-pm@vger.kernel.org, Viresh Kumar <viresh.kumar@linaro.org>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Leonard Crestez <leonard.crestez@nxp.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] cpufreq: Add user_min/max_freq
Date: Thu, 31 Oct 2019 15:23:56 -0700	[thread overview]
Message-ID: <20191031222356.GE27773@google.com> (raw)
In-Reply-To: <3169109.BFaCN5124U@kreacher>

On Thu, Oct 31, 2019 at 11:24:31AM +0100, Rafael J. Wysocki wrote:
> On Wednesday, October 30, 2019 1:41:49 AM CET Leonard Crestez wrote:
> > Current values in scaling_min_freq and scaling_max freq can change on
> > the fly due to event such as thermal monitoring.
> 
> Which is intentional.
> 
> > This behavior is confusing for userspace and because once an userspace
> > limit is written to scaling_min/max_freq it is not possible to read it back.
> 
> That can be argued both ways.
> 
> It is also useful to know the effective constraints and arguably the ability
> to read back the values that you have written is mostly needed for debugging
> the code.

Agreed that reading the values back is probably mostly useful for debugging.

Reading the effective constraints is a debugging use case as well, userspace
can't make any decisions based on values which might be in constant flux.

IMO the current interface is completely counterintuitive, I really hope we
wouldn't implement it the same way if given a chance to do it again. If there
is use for reading the effective constraints it should be exposed as a separate
read-only attribute. Keep it simple (when possible).

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2019-10-31 22:24 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-30  0:41 [PATCH] cpufreq: Add user_min/max_freq Leonard Crestez
2019-10-30  0:41 ` Leonard Crestez
2019-10-30 19:18 ` Matthias Kaehlcke
2019-10-30 19:18   ` Matthias Kaehlcke
2019-10-31 10:24 ` Rafael J. Wysocki
2019-10-31 10:24   ` Rafael J. Wysocki
2019-10-31 13:01   ` Leonard Crestez
2019-10-31 13:01     ` Leonard Crestez
2019-10-31 21:05     ` Rafael J. Wysocki
2019-10-31 21:05       ` Rafael J. Wysocki
2019-10-31 22:23   ` Matthias Kaehlcke [this message]
2019-10-31 22:23     ` Matthias Kaehlcke
2019-11-01 12:03     ` Rafael J. Wysocki
2019-11-01 12:03       ` Rafael J. Wysocki

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