On Tue, Oct 8, 2019 at 9:43 AM Giovanni Gherdovich <ggherdov...@suse.cz> wrote: > > On Thu, 2019-10-03 at 19:53 +0200, Rafael J. Wysocki wrote: > > On Thursday, October 3, 2019 2:15:37 PM CEST Peter Zijlstra wrote: > > > On Thu, Oct 03, 2019 at 12:27:52PM +0200, Rafael J. Wysocki wrote: > > > > On Wednesday, October 2, 2019 2:29:25 PM CEST Giovanni Gherdovich wrote: > > > > > +static bool turbo_disabled(void) > > > > > +{ > > > > > + u64 misc_en; > > > > > + int err; > > > > > + > > > > > + err = rdmsrl_safe(MSR_IA32_MISC_ENABLE, &misc_en); > > > > > + if (err) > > > > > + return false; > > > > > + > > > > > + return (misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE); > > > > > +} > > > > > > > > This setting may be updated by the platform firmware (BIOS) in some > > > > cases > > > > (see kernel.org BZ 200759, for example), so in general checking it once > > > > at the init time is not enough. > > > > > > Is there anything sane we can do if the BIOS frobs stuff like that under > > > our feet? Other than yell bloody murder, that is? > > > > Sane? No, I don't think so. > > > > Now, in principle *something* could be done to fix things up in the _PPC > > notify handler, but I guess we would just end up disabling the scale > > invariance code altogether in those cases. > > I'm looking at how to react to turbo being disabled at run time, assuming a > _PPC notification is triggered in that case. > > I don't think the correct action would be to disable scale invariance: if the > turbo range is not available, then max frequency is max_P, and scale > invariance can go on using that. The case max_freq=max_P is represented by > arch_max_freq=1024 in this patch (because arch_max_freq=max_freq*1024/max_P).
OK, so now you have the case when the BIOS enables turbo on the fly, but then the scale invariance is not going to be enabled AFAICS. > Since the variable arch_max_freq is global to all CPUs, the fact that the _PPC > notification is sent to just one CPU is not a concern: the CPU receiving the > notif will set arch_max_freq=1024 (Srinivas was worried about this in another > message). > > This looks like a job for the ->update_limits callback you added to "struct > cpufreq_driver" in response to the mentioned kernel.org BZ 200759. > I see that only intel_pstate implements it, it's not clear to me yet if I'll > have to give an ->update_limits to acpi_cpufreq as well to treat this case. If you want acpi_cpufreq and intel_pstate to be consistent with each other in that repsect, then yes.