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8e2f3bce05
According to Intel 64 and IA-32 Architectures SDM, Volume 3,
Chapter 14.2, "Software needs to exercise care to avoid delays
between the two RDMSRs (for example interrupts)".
So, disable interrupts during reading MSRs IA32_APERF and IA32_MPERF.
See also: commit 4ab60c3f32 (cpufreq: intel_pstate: Disable
interrupts during MSRs reading).
Signed-off-by: Doug Smythies <dsmythies@telus.net>
Reviewed-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
95 lines
2.1 KiB
C
95 lines
2.1 KiB
C
/*
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* x86 APERF/MPERF KHz calculation for
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* /sys/.../cpufreq/scaling_cur_freq
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*
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* Copyright (C) 2017 Intel Corp.
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* Author: Len Brown <len.brown@intel.com>
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*
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* This file is licensed under GPLv2.
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*/
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#include <linux/delay.h>
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#include <linux/ktime.h>
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#include <linux/math64.h>
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#include <linux/percpu.h>
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#include <linux/smp.h>
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struct aperfmperf_sample {
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unsigned int khz;
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ktime_t time;
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u64 aperf;
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u64 mperf;
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};
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static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
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#define APERFMPERF_CACHE_THRESHOLD_MS 10
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#define APERFMPERF_REFRESH_DELAY_MS 20
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#define APERFMPERF_STALE_THRESHOLD_MS 1000
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/*
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* aperfmperf_snapshot_khz()
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* On the current CPU, snapshot APERF, MPERF, and jiffies
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* unless we already did it within 10ms
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* calculate kHz, save snapshot
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*/
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static void aperfmperf_snapshot_khz(void *dummy)
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{
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u64 aperf, aperf_delta;
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u64 mperf, mperf_delta;
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struct aperfmperf_sample *s = this_cpu_ptr(&samples);
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ktime_t now = ktime_get();
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s64 time_delta = ktime_ms_delta(now, s->time);
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unsigned long flags;
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/* Don't bother re-computing within the cache threshold time. */
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if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
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return;
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local_irq_save(flags);
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rdmsrl(MSR_IA32_APERF, aperf);
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rdmsrl(MSR_IA32_MPERF, mperf);
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local_irq_restore(flags);
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aperf_delta = aperf - s->aperf;
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mperf_delta = mperf - s->mperf;
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/*
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* There is no architectural guarantee that MPERF
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* increments faster than we can read it.
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*/
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if (mperf_delta == 0)
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return;
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s->time = now;
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s->aperf = aperf;
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s->mperf = mperf;
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/* If the previous iteration was too long ago, discard it. */
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if (time_delta > APERFMPERF_STALE_THRESHOLD_MS)
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s->khz = 0;
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else
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s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
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}
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unsigned int arch_freq_get_on_cpu(int cpu)
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{
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unsigned int khz;
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if (!cpu_khz)
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return 0;
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if (!static_cpu_has(X86_FEATURE_APERFMPERF))
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return 0;
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smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
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khz = per_cpu(samples.khz, cpu);
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if (khz)
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return khz;
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msleep(APERFMPERF_REFRESH_DELAY_MS);
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smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
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return per_cpu(samples.khz, cpu);
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}
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