Re: [RESEND PATCH V9 3/7] cpufreq: amd-pstate: Enable amd-pstate preferred core supporting.

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Oct 16, 2023 at 11:50:34AM -0700, srinivas pandruvada wrote:

I'll respond to the rest tomorrow, it's far too late.

> > > Also, same question as to the amd folks; what serializes those
> > > static
> > > variables?
> > 
> > That's a good one.
> 
> This function which is checking static variables is called from cpufreq
> ->init callback. Which in turn is called from a function which is
> passed as startup() function pointer to
> cpuhp_setup_state_nocalls_cpuslocked().
> 
> I see that startup() callbacks are called under a mutex
> cpuhp_state_mutex for each present CPUs. So if some tear down happen,
> that is also protected by the same mutex. The assumption is here is
> that cpuhp_invoke_callback() in hotplug state machine is not called in
> parallel on two CPUs by the hotplug state machine. But I see activity
> on parallel bringup, so this is questionable now.

Parallel bringup should still serialise this. It mostly only does the
hardware bringup in parallel.

Having a pointer back to the cpu hotplug lock would make it easier to
untangle this code though.