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Date: Tue, 14 Nov 2017 23:47:00 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: WANG Chao <chao.wang@...oud.cn>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.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: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again
On Saturday, November 11, 2017 12:09:18 AM CET Rafael J. Wysocki wrote:
> On Fri, Nov 10, 2017 at 8:11 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > On Thu, Nov 9, 2017 at 2:30 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> >>
> >> c_start() can run aperfmperf_snapshot_khz() on all CPUs upfront (say
> >> in parallel), then wait for a while (say 5 ms; the current 20 ms wait
> >> is overkill) and then aperfmperf_snapshot_khz() can be run once on
> >> each CPU in show_cpuinfo() without taking the "stale cache" threshold
> >> into account.
> >
> > Yeah, that won't work.
>
> Indeed.
>
> > What could work is to do that "smp_call_function_many()" at open time,
> > and *not* set the "wait" flag, but do it entirely asynchronously.
>
> Right.
>
> > But I don't think that's an option for 4.14 ;(
>
> Agreed.
>
> > So I guess I'll have to revert.
>
> Sure thing (and I see that you've reverted it already).
>
> The reason why I wanted to fix this up before the final 4.14 is that
> the "cpu MHz" behavior is kind of inconsistent now (generally, it is
> either constant or the last requested frequency depending on the
> cpufreq configuration), but that's not a blocker by any measure IMO.
>
> Anyway, I'll try to come up with something better next week.
So what about the one below? It works for me as expected.
I'm not super-happy with the __weak thing, but I kind of prefer it to
adding an extra callback to struct seq_operations just for cpuinfo on x86.
---
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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