Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface.

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 03/19/2014 10:33 AM, Viresh Kumar wrote:
> On 18 March 2014 17:46, Srivatsa S. Bhat
> <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>> Agreed. As far as I understand, for ->target drivers, today we use GOV_STOP
>> to stop managing the CPU going offline. And for ->setpolicy drivers, we will
>> use this new callback to achieve the same goal.
> 
> So a better question would be: What's the purpose of ->stop() call for a policy?

Ideally, it should remove the outgoing CPU from the policy and "stop managing
that CPU", whatever that means to the driver (for intel_pstate, it means
setting it to min P state and destroying the timer).

> Stop managing CPUs of that policy?

Stop managing only the particular CPU going offline. IOW, we should somehow
communicate to the ->stop() callback that we are taking CPU 'x' offline.

If adding a ->stop() callback in the cpufreq_driver is not the best way to
achieve it, then lets think of an alternative. The way I look at it, this
new mechanism what we want, should allow ->setpolicy drivers to do what the
GOV_STOP will do for regular drivers. That is, allow it to "shutdown the
CPU from a cpufreq perspective", whatever that means to the driver.
We can think of a completely different way of achieving it, if ->stop()
is not suitable for that purpose.

> Or even do something on CPUs of a policy
> before CPUs are offlined?
> 
> Probably in the current solution Dirk is doing both these things..
> 
> And so I thought maybe its better not to restrict ->stop() to just
> setpolicy() drivers.


Regards,
Srivatsa S. Bhat