x86/aperfmperf: Integrate the fallback code from show_cpuinfo()

Due to the avoidance of IPIs to idle CPUs arch_freq_get_on_cpu() can return
0 when the last sample was too long ago.

show_cpuinfo() has a fallback to cpufreq_quick_get() and if that fails to
return cpu_khz, but the readout code for the per CPU scaling frequency in
sysfs does not.

Move that fallback into arch_freq_get_on_cpu() so the behaviour is the same
when reading /proc/cpuinfo and /sys/..../cur_scaling_freq.

Suggested-by: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Doug Smythies <dsmythies@telus.net>
Link: https://lore.kernel.org/r/87pml5180p.ffs@tglx

diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index b15c884..1f60a2b 100644 (file)
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -405,12 +405,12 @@ void arch_scale_freq_tick(void)
 unsigned int arch_freq_get_on_cpu(int cpu)
 {
        struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
+       unsigned int seq, freq;
        unsigned long last;
-       unsigned int seq;
        u64 acnt, mcnt;
 
        if (!cpu_feature_enabled(X86_FEATURE_APERFMPERF))
-               return 0;
+               goto fallback;
 
        do {
                seq = raw_read_seqcount_begin(&s->seq);
@@ -424,9 +424,13 @@ unsigned int arch_freq_get_on_cpu(int cpu)
         * which covers idle and NOHZ full CPUs.
         */
        if (!mcnt || (jiffies - last) > MAX_SAMPLE_AGE)
-               return 0;
+               goto fallback;
 
        return div64_u64((cpu_khz * acnt), mcnt);
+
+fallback:
+       freq = cpufreq_quick_get(cpu);
+       return freq ? freq : cpu_khz;
 }
 
 static int __init bp_init_aperfmperf(void)

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 0a0ee55..099b6f0 100644 (file)
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -86,12 +86,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
        if (cpu_has(c, X86_FEATURE_TSC)) {
                unsigned int freq = arch_freq_get_on_cpu(cpu);
 
-               if (!freq)
-                       freq = cpufreq_quick_get(cpu);
-               if (!freq)
-                       freq = cpu_khz;
-               seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
-                          freq / 1000, (freq % 1000));
+               seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
        }
 
        /* Cache size */