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SubjectRe: [PATCH 5/7] x86/tsc: Update cpufreq transition notifier to handle multiple CPUs
On Thu, Mar 14, 2019 at 7:43 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> The cpufreq core currently calls the cpufreq transition notifier
> callback once for each affected CPU. This is going to change soon and
> the cpufreq core will call the callback only once for each cpufreq
> policy. The callback must look at the newly added field in struct
> cpufreq_freqs, "cpus", which contains policy->related_cpus (both
> online/offline CPUs) and perform per-cpu actions for them if any.
>
> This patch updates time_cpufreq_notifier() to use the new "cpus" field,
> update per-cpu data for all the related CPUs and call set_cyc2ns_scale()
> for all online related_cpus.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> arch/x86/kernel/tsc.c | 31 ++++++++++++++++++++-----------
> 1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 3fae23834069..587a6aa72f38 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -956,28 +956,37 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> void *data)
> {
> struct cpufreq_freqs *freq = data;
> - unsigned long *lpj;
> -
> - lpj = &boot_cpu_data.loops_per_jiffy;
> -#ifdef CONFIG_SMP
> - if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> - lpj = &cpu_data(freq->cpu).loops_per_jiffy;
> -#endif
> + bool boot_cpu = !IS_ENABLED(CONFIG_SMP) || freq->flags & CPUFREQ_CONST_LOOPS;
> + unsigned long lpj;
> + int cpu;
>
> if (!ref_freq) {
> ref_freq = freq->old;
> - loops_per_jiffy_ref = *lpj;
> tsc_khz_ref = tsc_khz;
> +
> + if (boot_cpu)
> + loops_per_jiffy_ref = boot_cpu_data.loops_per_jiffy;
> + else
> + loops_per_jiffy_ref = cpu_data(cpumask_first(freq->cpus)).loops_per_jiffy;
> }
> +
> if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
> (val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
> - *lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
> -
> + lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
> tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
> +
> if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> mark_tsc_unstable("cpufreq changes");
>
> - set_cyc2ns_scale(tsc_khz, freq->cpu, rdtsc());
> + if (boot_cpu) {
> + boot_cpu_data.loops_per_jiffy = lpj;
> + } else {
> + for_each_cpu(cpu, freq->cpus)

This needs to iterate over policy->cpus or you change the behavior.

Not that it will matter a lot (x86 in one CPU per policy anyway in the
vast majority of cases), but it is a change nevertheless. Moreover,
I'm not even sure if doing that for offline CPUs makes sense.

> + cpu_data(cpu).loops_per_jiffy = lpj;
> + }
> +
> + for_each_cpu_and(cpu, freq->cpus, cpu_online_mask)
> + set_cyc2ns_scale(tsc_khz, cpu, rdtsc());
> }
>
> return 0;
> --

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