Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | RE: [patch 00/10] x86/cpu: Consolidate APERF/MPERF code | Date | Mon, 25 Apr 2022 17:45:42 +0200 |
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On Wed, Apr 20 2022 at 15:08, Doug Smythies wrote: > On 2022.04.19 14:11 Thomas Gleixner wrote: >>> That's because after the changes in this series scaling_cur_freq >>> returns 0 if the given CPU is idle. >> >> Which is sensible IMO as there is really no point in waking an idle CPU >> just to read those MSRs, then wait 20ms wake it up again to read those >> MSRs again. > > I totally agree. > It is the inconsistency for what is displayed as a function of driver/governor > that is my concern.
Raphael suggested to move the show_cpuinfo() logic into the a/mperf code. See below.
Thanks,
tglx --- Subject: x86/aperfmperf: Integrate the fallback code from show_cpuinfo() From: Thomas Gleixner <tglx@linutronix.de> Date: Mon, 25 Apr 2022 15:19:29 +0200
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> --- arch/x86/kernel/cpu/aperfmperf.c | 10 +++++++--- arch/x86/kernel/cpu/proc.c | 7 +------ 2 files changed, 8 insertions(+), 9 deletions(-)
--- 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 cp * 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) --- 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 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 */
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