Hi Kumar, > -----Original Message----- > From: [email protected] [mailto:linux-pm- > [email protected]] On Behalf Of Viresh Kumar > Sent: Monday, February 22, 2016 12:58 PM > To: Rafael Wysocki; Srinivas Pandruvada; Len Brown; Viresh Kumar > Cc: [email protected]; [email protected]; Joonas Lahtinen; > [email protected] > Subject: [PATCH] intel-pstate: Update frequencies of policy->cpus only from > ->set_policy() > > The intel-pstate driver is using intel_pstate_hwp_set() from two separate > paths, i.e. ->set_policy() callback and sysfs update path for the files > present > in /sys/devices/system/cpu/intel_pstate/ directory. > > While an update to the sysfs path applies to all the CPUs being managed by > the driver (which essentially means all the online CPUs), the update via the - > >set_policy() callback applies to a smaller group of CPUs managed by the > policy for which ->set_policy() is called. > > And so, intel_pstate_hwp_set() should update frequencies of only the CPUs > that are part of policy->cpus mask, while it is called from > ->set_policy() callback. > > In order to do that, add a parameter (cpumask) to intel_pstate_hwp_set() > and apply the frequency changes only to the concerned CPUs. > > For ->set_policy() path, we are only concerned about policy->cpus, and so > policy->rwsem lock taken by the core prior to calling ->set_policy() is enough > to take care of any races. The larger lock acquired by > get_online_cpus() is required only for the updates to sysfs files. > IIRC, 1.HWP is hardwarely per-package, CPUs inside one package have one shared HWP. 2.Currently all the CPUs share the same HWP settings according to intel_pstate design. 3. The policy is per-cpu in intel_pstate driver.(policy->cpus only contains one cpu)
So with this patch applied, it is likely CPUs may have different HWP settings? For example: CPU 0 belongs to package A with policy 0, and CPU 1 belongs to package B with policy 1, If you change the policy 0 from powersave to performance, then only CPU0 will update its min/max freq in HWP, however we should also update CPU 2's min/max in HWP settings? Plz correct me if I'm wrong.. thanks, yu
