Re: [PATCH v3 07/11] x86/intel_pstate: changes in cpufreq_del_cpu for CPU offline

["Wang, Wei W" <wei.w.wang@intel.com>]

On 11/06/2015 22:06, Julien Grall wrote:
> On 11/06/2015 04:28, Wei Wang wrote:
> > cpufreq_cpu_policy is used in intel_pstate_set_pstate(), so we change
> > to NULL it after the call of cpufreq_driver->exit. Otherwise, a
> > calltrace will show up on your screen due to the reference of a NULL
> > pointer when you power down the system.
> >
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > ---
> >   xen/drivers/cpufreq/cpufreq.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/xen/drivers/cpufreq/cpufreq.c
> > b/xen/drivers/cpufreq/cpufreq.c index 6003a8c..a8772e8 100644
> > --- a/xen/drivers/cpufreq/cpufreq.c
> > +++ b/xen/drivers/cpufreq/cpufreq.c
> > @@ -335,12 +335,11 @@ int cpufreq_del_cpu(unsigned int cpu)
> >
> >       /* for HW_ALL, stop gov for each core of the _PSD domain */
> >       /* for SW_ALL & SW_ANY, stop gov for the 1st core of the _PSD domain
> */
> > -    if (hw_all || (cpumask_weight(cpufreq_dom->map) ==
> > -                   perf->domain_info.num_processors))
> > +    if (!policy->policy && (hw_all || (cpumask_weight(cpufreq_dom->map)
> ==
> > +                   perf->domain_info.num_processors)))
> 
> Based on your patch #6, the field policy contains value which is defined per-
> cpufreq driver (because you defined internal value). How can you be sure
> that a driver will never use 0 as a valid value?

Hi Julien, what do you mean by "per-cpufreq driver"? 

We currently have two P-state drivers. This filed is currently only used by the intel_pstate driver, and the four usable values are:
#define CPUFREQ_POLICY_POWERSAVE           (1)
#define CPUFREQ_POLICY_PERFORMANCE      (2)
#define CPUFREQ_POLICY_USERSPACE              (3)
#define CPUFREQ_POLICY_ONDEMAND            (4)

The intel_pstate won't use 0 as a valid value, and the default value is CPUFREQ_POLICY_ONDEMAND.  If it's 0, it basically means the old acpi-cpufreq driver is being used.

Best,
Wei