Re: [PATCH 1/2] cpufreq: serialize calls to __cpufreq_governor()

["Robert Schöne" <robert.schoene@tu-dresden.de>]

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> Robert/Prarit,
> 
> I thought you guys would test this very quickly as it had been hanging since
> long time. What happened ?
> 
> > Hey Viresh, this is on my plate for today.  It does look like the panic I sent
> > you yesterday in email does occur when your patches are put into the latest
> > upstream kernel :(.
> 
> I have tested my patches over mainline only, i.e. v3.17 .
> 
> Even the branch I mentioned above is based on that.

Hi,

This patch makes it worse. Even when changing the governors sequentially
for all CPUs, it fails. Here is what happens:

1. I boot the system. (performance)
2. An Ubuntu service enables ondemand sequentially for all cpus (ondemand)
3. I enable performance sequentially (performance)
4. I enable ondemand sequentially (broken)
In the last step, ondemand can only be enabled at a single CPU. All others return -EBUSY.


More about step 3/4:
$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
performance
performance
performance
performance
performance
performance
performance
performance
$ echo ondemand | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
ondemand
$ echo ondemand | sudo tee /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
ondemand
tee: /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor: Device or resource busy


Robert

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