Re: [PATCH RFC] Revert "cpufreq: dt: Identify cpu-sharing for platforms without operating-points-v2"

[Alexandre Courbot]

On 06/16/2016 03:35 PM, Viresh Kumar wrote:
> +Rafael
>
> On 16-06-16, 14:35, Alexandre Courbot wrote:
> > This is not an actual request for revert, but rather for comments about
> > the observed behavior since I am not really familiar with cpufreq.
> >
> > I am observing a serious performance regression on Jetson TK1 since 4.7-rc1:
> > namely, moving windows under X would become unsufferably slow, and graphical
> > performance under X in general is seriously degraded. After bisecting, I
> > found the regression to be visible since commit 1530b9963eeb ("cpufreq: dt:
> > Identify cpu-sharing for platforms without operating-points-v2")
> >
> > If I revert this commit, I noticed that the CPU frequency immediately jumps to
> > a higher frequency once I start moving windows (resulting in a smooth and
> > responsive action), whereas enabling this commit causes the CPU frequency to
> > remain low (typically 204 Mhz) in that case, resulting in CPU-bound slowness.
> >
> > What happens is that with 1530b9963eeb applied, dev_pm_opp_get_sharing_cpus()
> > returns zero causing the fallback variable to remain false, whereas without it
> > opp_v1 is set to true.
> >
> > It is not clear to me whether this is a cpufreq issue or a Tegra issue, so I am
> > posting this in the hope to get clarifications from either side.
> >
> > Thanks!
>
> Yeah, you just hit a corner case. Sorry about that :(
>
> Can you try a patch that I sent to you instead? Its subject is:
>
> [PATCH] PM / OPP: 'UNKNOWN' status of opp-table->shared

Thanks, this seems to solve the issue.

> Also I would like to know one more thing. You can hit this bug only if
> some other piece of code for your platform is creating OPP table for
> the CPUs. Which code is doing that ?

Good question. I am still educating myself about OPP - adding Thierry in 
the meantime who may have an answer.