summaryrefslogtreecommitdiffstats
path: root/arch
diff options
context:
space:
mode:
authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-07-28 14:45:03 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-07-30 14:26:51 +0200
commit4815d3c56d1e10449a44089a47544d9ba84fad0d (patch)
tree4b0c96b189ce8a66b7ded6301480a99489b2e9d2 /arch
parent520eccdfe187591a51ea9ab4c1a024ae4d0f68d9 (diff)
downloadlinux-4815d3c56d1e10449a44089a47544d9ba84fad0d.tar.bz2
cpufreq: x86: Make scaling_cur_freq behave more as expected
After commit f8475cef9008 "x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF" the scaling_cur_freq policy attribute in sysfs only behaves as expected on x86 with APERF/MPERF registers available when it is read from at least twice in a row. The value returned by the first read may not be meaningful, because the computations in there use cached values from the previous iteration of aperfmperf_snapshot_khz() which may be stale. To prevent that from happening, modify arch_freq_get_on_cpu() to call aperfmperf_snapshot_khz() twice, with a short delay between these calls, if the previous invocation of aperfmperf_snapshot_khz() was too far back in the past (specifically, more that 1s ago). Also, as pointed out by Doug Smythies, aperf_delta is limited now and the multiplication of it by cpu_khz won't overflow, so simplify the s->khz computations too. Fixes: f8475cef9008 "x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF" Reported-by: Doug Smythies <dsmythies@telus.net> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/cpu/aperfmperf.c40
1 files changed, 26 insertions, 14 deletions
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index d869c8671e36..7cf7c70b6ef2 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -8,20 +8,25 @@
* This file is licensed under GPLv2.
*/
-#include <linux/jiffies.h>
+#include <linux/delay.h>
+#include <linux/ktime.h>
#include <linux/math64.h>
#include <linux/percpu.h>
#include <linux/smp.h>
struct aperfmperf_sample {
unsigned int khz;
- unsigned long jiffies;
+ ktime_t time;
u64 aperf;
u64 mperf;
};
static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
+#define APERFMPERF_CACHE_THRESHOLD_MS 10
+#define APERFMPERF_REFRESH_DELAY_MS 20
+#define APERFMPERF_STALE_THRESHOLD_MS 1000
+
/*
* aperfmperf_snapshot_khz()
* On the current CPU, snapshot APERF, MPERF, and jiffies
@@ -33,9 +38,11 @@ static void aperfmperf_snapshot_khz(void *dummy)
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);
- /* Don't bother re-computing within 10 ms */
- if (time_before(jiffies, s->jiffies + HZ/100))
+ /* Don't bother re-computing within the cache threshold time. */
+ if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
return;
rdmsrl(MSR_IA32_APERF, aperf);
@@ -51,22 +58,21 @@ static void aperfmperf_snapshot_khz(void *dummy)
if (mperf_delta == 0)
return;
- /*
- * if (cpu_khz * aperf_delta) fits into ULLONG_MAX, then
- * khz = (cpu_khz * aperf_delta) / mperf_delta
- */
- if (div64_u64(ULLONG_MAX, cpu_khz) > aperf_delta)
- s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
- else /* khz = aperf_delta / (mperf_delta / cpu_khz) */
- s->khz = div64_u64(aperf_delta,
- div64_u64(mperf_delta, cpu_khz));
- s->jiffies = jiffies;
+ s->time = now;
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);
}
unsigned int arch_freq_get_on_cpu(int cpu)
{
+ unsigned int khz;
+
if (!cpu_khz)
return 0;
@@ -74,6 +80,12 @@ unsigned int arch_freq_get_on_cpu(int cpu)
return 0;
smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
+ khz = per_cpu(samples.khz, cpu);
+ if (khz)
+ return khz;
+
+ msleep(APERFMPERF_REFRESH_DELAY_MS);
+ smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
return per_cpu(samples.khz, cpu);
}