linux-kernel - Re: [PATCH] Revert "cpufreq: pcc-cpufreq: update default value of cpuinfo_transition

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Message-ID: <CAJZ5v0g3_QrVD3rwjdcWKcDb5SpA11n9C_2Jpk6qMsXg3pxfOg@mail.gmail.com>
Date:	Sat, 23 Jul 2016 01:47:26 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andreas Herrmann <aherrmann@...e.com>,
	Jacob Tanenbaum <jtanenba@...hat.com>,
	Stable <stable@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "cpufreq: pcc-cpufreq: update default value of cpuinfo_transition_latency"

On Sat, Jul 23, 2016 at 1:30 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 22-07-16, 23:46, Rafael J. Wysocki wrote:
>> On Friday, July 22, 2016 02:28:52 PM Viresh Kumar wrote:
>> > On 22-07-16, 23:31, Rafael J. Wysocki wrote:
>> > > > cpufreq.c
>> > > >
>> > > >         if (policy->governor->max_transition_latency &&
>> > > >             policy->cpuinfo.transition_latency >
>> > > >             policy->governor->max_transition_latency) {
>> > > >
>> > > > - And this check will always fail, unless max_transition_latency is zero.
>> > >
>> > > Why would it fail?  If governor->max_transition_latency is non-zero, but less
>> > > than UNIT_MAX, the condition checked will be true to my eyes.
>> >
>> > Bad wording. Sorry.
>> >
>> > I meant, this 'if' check will always succeed (as you also noted), and
>> > so we will always get the error message reported in this patch.
>>
>> Not always, but for drivers setting cpuinfo.transition_latency to CPUFREQ_ETERNAL.
>
> So the drivers which have set their transition_latency to
> CPUFREQ_ETERNAL, can't use ondemand governor unless
> governor->max_transition_latency is set to 0 from userspace.
>
> What should be done about this patch then ? It broke in late 2015.

I'll apply the revert with a "Cc: stable" tag.

Question is what to do about the other drivers setting
cpuinfo.transition_latency to CPUFREQ_ETERNAL.

Thanks,
Rafael