Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

[Saravana Kannan]

On 08/01/2014 12:54 PM, Stephen Boyd wrote:
> On 08/01/14 12:43, Prarit Bhargava wrote:
> > On 08/01/2014 03:36 PM, Stephen Boyd wrote:
> > > On 08/01/14 12:15, Prarit Bhargava wrote:
> > > > On 08/01/2014 01:18 PM, Stephen Boyd wrote:
> > > > > On 08/01/14 03:27, Prarit Bhargava wrote:
> > > > > > Can you send me the test and the trace of the deadlock?  I'm not creating it with:
> > > > > This was with conservative as the default, and switching to ondemand
> > > > >
> > > > > # cd /sys/devices/system/cpu/cpu2/cpufreq
> > > > > # ls
> > > > > affected_cpus                  scaling_available_governors
> > > > > conservative                   scaling_cur_freq
> > > > > cpuinfo_cur_freq               scaling_driver
> > > > > cpuinfo_max_freq               scaling_governor
> > > > > cpuinfo_min_freq               scaling_max_freq
> > > > > cpuinfo_transition_latency     scaling_min_freq
> > > > > related_cpus                   scaling_setspeed
> > > > > scaling_available_frequencies  stats
> > > > > # cat conservative/down_threshold
> > > > > 20
> > > > > # echo ondemand > scaling_governor
> > > > Thanks Stephen,
> > > >
> > > > There's obviously a difference in our .configs.  I have a global conservative
> > > > directory, ie) /sys/devices/system/cpu/cpufreq/conservative instead of a per-cpu
> > > > governor file.
> > > >
> > > > ie) what are your .config options for CPUFREQ?
> > > >
> > > > Mine are:
> > > >
> > > > #
> > > > # CPU Frequency scaling
> > > > #
> > > > CONFIG_CPU_FREQ=y
> > > > CONFIG_CPU_FREQ_GOV_COMMON=y
> > > > CONFIG_CPU_FREQ_STAT=m
> > > > CONFIG_CPU_FREQ_STAT_DETAILS=y
> > > > # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
> > > > # CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
> > > > # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
> > > > CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE=y
> > > > CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
> > > > CONFIG_CPU_FREQ_GOV_POWERSAVE=y
> > > > CONFIG_CPU_FREQ_GOV_USERSPACE=y
> > > > CONFIG_CPU_FREQ_GOV_ONDEMAND=y
> > > > CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
> > > >
> > > > Is there some other config option I have to set?
> > > I have the same options. The difference is that my driver has a governor
> > > per policy. That's set with the CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag.
> > > If I remove that flag I can't trigger the lockdep splat anymore with
> > > this sequence and your patch.
> > I see -- so you're seeing this on arm then?  If so, let me know so I can reserve
> > one to work on :)
>
> I only have ARM to test on. You can set this flag in your cpufreq driver
> if you have independently scaling CPU frequencies, so it isn't
> necessarily an ARM thing.

Sorry, forgot to mention this in the earlier email. But yeah, this is a 
totally SW feature. You should be able to enable this flag in your driver.

-Saravana

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