Messages in this thread | | | Date | Wed, 19 Mar 2014 15:30:48 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface. |
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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
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