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Message-ID: <20171115093347.GA28750@WANG-Chaos-MacBook-Pro.local>
Date: Wed, 15 Nov 2017 17:33:47 +0800
From: WANG Chao <chao.wang@...oud.cn>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
Kate Stewart <kstewart@...uxfoundation.org>,
Len Brown <len.brown@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Philippe Ombredanne <pombredanne@...b.com>,
Mathias Krause <minipli@...glemail.com>,
the arch/x86 maintainers <x86@...nel.org>,
Linux PM <linux-pm@...r.kernel.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] x86 / CPU: Always show current CPU frequency in
/proc/cpuinfo
On 11/15/17 at 02:13P, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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.wysocki@...el.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,
>
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