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

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Message-ID: <20160722233042.GI3122@ubuntu>
Date:	Fri, 22 Jul 2016 16:30:42 -0700
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Andreas Herrmann <aherrmann@...e.com>,
	Jacob Tanenbaum <jtanenba@...hat.com>, stable@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "cpufreq: pcc-cpufreq: update default value of
 cpuinfo_transition_latency"

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.

-- 
viresh