On 11/15/17 at 02:13P, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > After commit 890da9cf0983 (Revert "x86: do not use cpufreq_quick_get() > for /proc/cpuinfo "cpu MHz"") the "cpu MHz" number in /proc/cpuinfo > on x86 can be either the nominal CPU frequency (which is constant) > or the frequency most recently requested by a scaling governor in > cpufreq, depending on the cpufreq configuration. That is somewhat > inconsistent and is different from what it was before 4.13, so in > order to restore the previous behavior, make it report the current > CPU frequency like the scaling_cur_freq sysfs file in cpufreq. > > To that end, modify the /proc/cpuinfo implementation on x86 to use > aperfmperf_snapshot_khz() to snapshot the APERF and MPERF feedback > registers, if available, and use their values to compute the CPU > frequency to be reported as "cpu MHz". > > However, do that carefully enough to avoid accumulating delays that > lead to unacceptable access times for /proc/cpuinfo on systems with > many CPUs. Run aperfmperf_snapshot_khz() once on all CPUs > asynchronously at the /proc/cpuinfo open time, add a single delay > upfront (if necessary) at that point and simply compute the current > frequency while running show_cpuinfo() for each individual CPU.
Hi, Rafael I tested your patch. It's much faster. But from what I got, calling aperfmperf_snapshot_khz() asynchronously with 10ms sleep takes much longer than calling aperfmperf_snapshot_khz() synchronously. Here's my result on 64 CPUs: - async aperfmperf_snapshot_khz() w/ 10ms sleep: # time cat /proc/cpuinfo > /dev/null real 0m0.014s user 0m0.000s sys 0m0.002s - sync aperfmperf_snapshot_khz() w/o any sleep: # time cat /proc/cpuinfo > /dev/null real 0m0.002s user 0m0.000s sys 0m0.002s Thanks, WANG Chao > > Also, to avoid slowing down /proc/cpuinfo accesses too much, reduce > the default delay between consecutive APERF and MPERF reads to 10 ms, > which should be sufficient to get large enough numbers for the > frequency computation in all cases. > > Fixes: 890da9cf0983 (Revert "x86: do not use cpufreq_quick_get() for > /proc/cpuinfo "cpu MHz"") > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > --- > > Resent with a changelog & tags. > > I'm going to route it via the linux-pm tree. > > --- > arch/x86/kernel/cpu/aperfmperf.c | 74 > +++++++++++++++++++++++++++------------ > arch/x86/kernel/cpu/cpu.h | 3 + > arch/x86/kernel/cpu/proc.c | 6 ++- > fs/proc/cpuinfo.c | 6 +++ > include/linux/cpufreq.h | 1 > 5 files changed, 67 insertions(+), 23 deletions(-) > > Index: linux-pm/arch/x86/kernel/cpu/proc.c > =================================================================== > --- linux-pm.orig/arch/x86/kernel/cpu/proc.c > +++ linux-pm/arch/x86/kernel/cpu/proc.c > @@ -5,6 +5,8 @@ > #include <linux/seq_file.h> > #include <linux/cpufreq.h> > > +#include "cpu.h" > + > /* > * Get CPU information for use by the procfs. > */ > @@ -78,9 +80,11 @@ static int show_cpuinfo(struct seq_file > seq_printf(m, "microcode\t: 0x%x\n", c->microcode); > > if (cpu_has(c, X86_FEATURE_TSC)) { > - unsigned int freq = cpufreq_quick_get(cpu); > + unsigned int freq = aperfmperf_get_khz(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)); > Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c > =================================================================== > --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c > +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c > @@ -14,6 +14,8 @@ > #include <linux/percpu.h> > #include <linux/smp.h> > > +#include "cpu.h" > + > struct aperfmperf_sample { > unsigned int khz; > ktime_t time; > @@ -24,7 +26,7 @@ struct aperfmperf_sample { > static DEFINE_PER_CPU(struct aperfmperf_sample, samples); > > #define APERFMPERF_CACHE_THRESHOLD_MS 10 > -#define APERFMPERF_REFRESH_DELAY_MS 20 > +#define APERFMPERF_REFRESH_DELAY_MS 10 > #define APERFMPERF_STALE_THRESHOLD_MS 1000 > > /* > @@ -38,8 +40,6 @@ static void aperfmperf_snapshot_khz(void > u64 aperf, aperf_delta; > u64 mperf, mperf_delta; > struct aperfmperf_sample *s = this_cpu_ptr(&samples); > - ktime_t now = ktime_get(); > - s64 time_delta = ktime_ms_delta(now, s->time); > unsigned long flags; > > local_irq_save(flags); > @@ -57,38 +57,68 @@ static void aperfmperf_snapshot_khz(void > if (mperf_delta == 0) > return; > > - s->time = now; > + s->time = ktime_get(); > s->aperf = aperf; > s->mperf = mperf; > - > - /* If the previous iteration was too long ago, discard it. */ > - if (time_delta > APERFMPERF_STALE_THRESHOLD_MS) > - s->khz = 0; > - else > - s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta); > + s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta); > } > > -unsigned int arch_freq_get_on_cpu(int cpu) > +static bool aperfmperf_snapshot_cpu(int cpu, ktime_t now, bool wait) > { > - s64 time_delta; > - unsigned int khz; > + s64 time_delta = ktime_ms_delta(now, per_cpu(samples.time, cpu)); > + > + /* Don't bother re-computing within the cache threshold time. */ > + if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS) > + return true; > + > + smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, wait); > + > + /* Return false if the previous iteration was too long ago. */ > + return time_delta <= APERFMPERF_STALE_THRESHOLD_MS; > +} > > +unsigned int aperfmperf_get_khz(int cpu) > +{ > if (!cpu_khz) > return 0; > > if (!static_cpu_has(X86_FEATURE_APERFMPERF)) > return 0; > > - /* Don't bother re-computing within the cache threshold time. */ > - time_delta = ktime_ms_delta(ktime_get(), per_cpu(samples.time, cpu)); > - khz = per_cpu(samples.khz, cpu); > - if (khz && time_delta < APERFMPERF_CACHE_THRESHOLD_MS) > - return khz; > + aperfmperf_snapshot_cpu(cpu, ktime_get(), true); > + return per_cpu(samples.khz, cpu); > +} > > - smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1); > - khz = per_cpu(samples.khz, cpu); > - if (khz) > - return khz; > +void arch_freq_prepare_all(void) > +{ > + ktime_t now = ktime_get(); > + bool wait = false; > + int cpu; > + > + if (!cpu_khz) > + return; > + > + if (!static_cpu_has(X86_FEATURE_APERFMPERF)) > + return; > + > + for_each_online_cpu(cpu) > + if (!aperfmperf_snapshot_cpu(cpu, now, false)) > + wait = true; > + > + if (wait) > + msleep(APERFMPERF_REFRESH_DELAY_MS); > +} > + > +unsigned int arch_freq_get_on_cpu(int cpu) > +{ > + if (!cpu_khz) > + return 0; > + > + if (!static_cpu_has(X86_FEATURE_APERFMPERF)) > + return 0; > + > + if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true)) > + return per_cpu(samples.khz, cpu); > > msleep(APERFMPERF_REFRESH_DELAY_MS); > smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1); > Index: linux-pm/arch/x86/kernel/cpu/cpu.h > =================================================================== > --- linux-pm.orig/arch/x86/kernel/cpu/cpu.h > +++ linux-pm/arch/x86/kernel/cpu/cpu.h > @@ -47,4 +47,7 @@ extern const struct cpu_dev *const __x86 > > extern void get_cpu_cap(struct cpuinfo_x86 *c); > extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c); > + > +unsigned int aperfmperf_get_khz(int cpu); > + > #endif /* ARCH_X86_CPU_H */ > Index: linux-pm/fs/proc/cpuinfo.c > =================================================================== > --- linux-pm.orig/fs/proc/cpuinfo.c > +++ linux-pm/fs/proc/cpuinfo.c > @@ -1,12 +1,18 @@ > // SPDX-License-Identifier: GPL-2.0 > +#include <linux/cpufreq.h> > #include <linux/fs.h> > #include <linux/init.h> > #include <linux/proc_fs.h> > #include <linux/seq_file.h> > > +__weak void arch_freq_prepare_all(void) > +{ > +} > + > extern const struct seq_operations cpuinfo_op; > static int cpuinfo_open(struct inode *inode, struct file *file) > { > + arch_freq_prepare_all(); > return seq_open(file, &cpuinfo_op); > } > > Index: linux-pm/include/linux/cpufreq.h > =================================================================== > --- linux-pm.orig/include/linux/cpufreq.h > +++ linux-pm/include/linux/cpufreq.h > @@ -917,6 +917,7 @@ static inline bool policy_has_boost_freq > } > #endif > > +extern void arch_freq_prepare_all(void); > extern unsigned int arch_freq_get_on_cpu(int cpu); > > extern void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq, >