On Tue, Mar 19, 2019 at 11:49 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 19-03-19, 10:41, Rafael J. Wysocki wrote:
> > On Tue, Mar 19, 2019 at 6:50 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> > >
> > > On 18-03-19, 12:49, Rafael J. Wysocki wrote:
> > > > To summarize, I think that it would be sufficient to do this just for
> > > > policy->cpu and, as Peter said, warn once if there are more CPUs in
> > > > the policy or policy->cpu is not the CPU running this code. And mark
> > > > the TSC as unstable in both of these cases.
> > >
> > > How about this ?
> >
> > We guarantee that this will always run on policy->cpu IIRC, so it LGTM
>
> Yeah, the governor guarantees that unless dvfs_possible_from_any_cpu is set for
> the policy. But there are few direct invocations to cpufreq_driver_target() and
> __cpufreq_driver_target() which don't take that into account. First one is done
> from cpufreq_online(), which can get called on any CPU I believe. Other one is
> from cpufreq_generic_suspend(). But I think none of them gets called for x86 and
> so below code should be safe.
I meant on x86, sorry.
> > overall, but the new message is missing "one".
>
> Talking about print message ?
Yes.
> > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > > index 3fae23834069..4d3681cfb6e0 100644
> > > --- a/arch/x86/kernel/tsc.c
> > > +++ b/arch/x86/kernel/tsc.c
> > > @@ -958,10 +958,13 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> > > struct cpufreq_freqs *freq = data;
> > > unsigned long *lpj;
> > >
> > > + if (WARN_ON_ONCE(cpumask_weight(freq->policy->related_cpus) != 1))
> > > + mark_tsc_unstable("cpufreq policy has more than CPU");
> >
> > Also I would check policy->cpus here. After all, we don't care about
> > CPUs that are never online.
>
> Because the CPU isn't in the policy->cpus mask, we can't say it was *never*
> online. Just that it isn't online at that moment of time. I used related_cpus as
> the code here should be robust against any corner cases and shouldn't have
> different behavior based on value of policy->cpus.
>
> If the cpufreq driver is probed after all but one CPUs of a policy are offlined,
> then you won't see the warning if policy->cpus is used. But the warning will
> appear if any other CPU is onlined. For me that is wrong, we should have got the
> warning earlier as well as it was just wrong to not warn earlier.
Fair enough.
> > And the message could be something like "cpufreq changes: related CPUs
> > affected".
>
> Sure.
>
> I also forgot to add a "return" statement here. We shouldn't continue in this
> case, right ?
It makes a little sense to continue then, so it's better to return
immediately in that case IMO.
> > > +
> > > lpj = &boot_cpu_data.loops_per_jiffy;
> > > #ifdef CONFIG_SMP
> > > if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> > > - lpj = &cpu_data(freq->cpu).loops_per_jiffy;
> > > + lpj = &cpu_data(freq->policy->cpu).loops_per_jiffy;
> > > #endif
> > >
> > > if (!ref_freq) {
> > > @@ -977,7 +980,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> > > if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> > > mark_tsc_unstable("cpufreq changes");
> > >
> > > - set_cyc2ns_scale(tsc_khz, freq->cpu, rdtsc());
> > > + set_cyc2ns_scale(tsc_khz, freq->policy->cpu, rdtsc());
> > > }
> > >
> > > return 0;
