This is a note to let you know that I've just added the patch titled
x86 / CPU: Always show current CPU frequency in /proc/cpuinfo
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-cpu-always-show-current-cpu-frequency-in-proc-cpuinfo.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 7d5905dc14a87805a59f3c5bf70173aac2bb18f8 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" rafael.j.wysocki@intel.com Date: Wed, 15 Nov 2017 02:13:40 +0100 Subject: x86 / CPU: Always show current CPU frequency in /proc/cpuinfo
From: Rafael J. Wysocki rafael.j.wysocki@intel.com
commit 7d5905dc14a87805a59f3c5bf70173aac2bb18f8 upstream.
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.
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.wysocki@intel.com Acked-by: Thomas Gleixner tglx@linutronix.de Tested-by: Thomas Gleixner tglx@linutronix.de Acked-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/cpu/Makefile | 2 - 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 6 files changed, 68 insertions(+), 24 deletions(-)
--- a/arch/x86/kernel/cpu/Makefile +++ b/arch/x86/kernel/cpu/Makefile @@ -22,7 +22,7 @@ obj-y += common.o obj-y += rdrand.o obj-y += match.o obj-y += bugs.o -obj-$(CONFIG_CPU_FREQ) += aperfmperf.o +obj-y += aperfmperf.o obj-y += cpuid-deps.o
obj-$(CONFIG_PROC_FS) += proc.o --- a/arch/x86/kernel/cpu/aperfmperf.c +++ b/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); --- a/arch/x86/kernel/cpu/cpu.h +++ b/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 */ --- a/arch/x86/kernel/cpu/proc.c +++ b/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)); --- a/fs/proc/cpuinfo.c +++ b/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); }
--- a/include/linux/cpufreq.h +++ b/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);
/* the following are really really optional */
Patches currently in stable-queue which might be from rafael.j.wysocki@intel.com are
queue-4.14/x86-cpu-always-show-current-cpu-frequency-in-proc-cpuinfo.patch queue-4.14/x86-cpu-avoid-unnecessary-ipis-in-arch_freq_get_on_cpu.patch