linux-kernel - Re: "cpufreq: fix serialization issues with freq change notifiers" breaks cpufreq too

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Date:	Tue, 10 Sep 2013 01:12:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, Greg KH <greg@...ah.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-pm@...r.kernel.org, cpufreq@...r.kernel.org,
	linux-sh@...r.kernel.org, Magnus Damm <magnus.damm@...il.com>
Subject: Re: "cpufreq: fix serialization issues with freq change notifiers" breaks cpufreq too

On Monday, September 09, 2013 11:42:41 PM Guennadi Liakhovetski wrote:
> Hi Rafael
> 
> On Mon, 9 Sep 2013, Rafael J. Wysocki wrote:
> 
> > Hi,
> > 
> > On Monday, September 09, 2013 05:11:10 PM Guennadi Liakhovetski wrote:
> > > Sorry guys, I'm trying my best to stop this patch from propagating to 
> > > stable and to get it fixed asap, so, the CC list might be a bit excessive. 
> > > Also trying to fix the originally spare cc list, which makes it impossible 
> > > for me to reply to the original thread, instead have to start a new one.
> > 
> > I'm not sure what you're talking about.  What exactly was wrong with the
> > original CC list in particular?
> 
> I think you advised once to cc cpufreq related mails to linux-pm too at 
> least.

Yes, I did.

> I haven't found this patch in my pm archive, have I missed it there?

Quite frankly, I don't remember if it was there.  ISTR having it it patchwork,
which would mean that it was there, but well.

> > > Commit
> > > 
> > > commit dceff5ce18801dddc220d6238628619c93bc3cb6
> > > Author: Viresh Kumar <viresh.kumar@...aro.org>
> > > Date:   Sun Sep 1 22:19:37 2013 +0530
> > > 
> > >     cpufreq: fix serialization issues with freq change notifiers
> > > 
> > > breaks .transition_ongoing counting.
> > 
> > Do you know how exactly it breaks that?  If so, care to share that knowledge?
> 
> No, I don't. I only know that in __cpufreq_driver_target() the check for
> 
> 	if (policy->transition_ongoing) {
> 		write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> 		return -EBUSY;
> 	}
> 
> is failing with this patch and cpufreq-cpu0.

OK, we need to figure out that, then.

> > > This leads to cpufreq-cpu0 not working any more. In particular switching the
> > > governor from performance to powersave directly after boot doesn't result in
> > > a frequency switch any more. Reverting this patch fixes the problem again.
> > 
> > However, this is a regression fix, so I'd prefer to fix the problem on top of
> > it instead of reverting this commit entirely.
> 
> If I understood correctly, this patch fixed some warnings, that, however, 
> didn't disrupt functionality, is this right? Whereas the patch really 
> seems to break working set ups.

It fixed warnings that indicated problems and those problems should rather be
avoided.

Thanks,
Rafael

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