cpupower: mperf monitor - Use TSC to calculate max frequency if possible

Which makes the implementation independent from cpufreq drivers.
Therefore this would also work on a Xen kernel where the hypervisor
is doing frequency switching and idle entering.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 130 insertions, 47 deletions

diff --git a/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c b/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c
index 63ca87a05e5f..5650ab5a2c20 100644
--- a/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c
+++ b/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c
@@ -22,12 +22,15 @@
 
 #define MSR_TSC 0x10
 
+#define MSR_AMD_HWCR 0xc0010015
+
 enum mperf_id { C0 = 0, Cx, AVG_FREQ, MPERF_CSTATE_COUNT };
 
 static int mperf_get_count_percent(unsigned int self_id, double *percent,
                                    unsigned int cpu);
 static int mperf_get_count_freq(unsigned int id, unsigned long long *count,
                                 unsigned int cpu);
+static struct timespec time_start, time_end;
 
 static cstate_t mperf_cstates[MPERF_CSTATE_COUNT] = {
         {
@@ -54,19 +57,33 @@ static cstate_t mperf_cstates[MPERF_CSTATE_COUNT] = {
         },
 };
 
+enum MAX_FREQ_MODE { MAX_FREQ_SYSFS, MAX_FREQ_TSC_REF };
+static int max_freq_mode;
+/*
+ * The max frequency mperf is ticking at (in C0), either retrieved via:
+ *   1) calculated after measurements if we know TSC ticks at mperf/P0 frequency
+ *   2) cpufreq /sys/devices/.../cpu0/cpufreq/cpuinfo_max_freq at init time
+ * 1. Is preferred as it also works without cpufreq subsystem (e.g. on Xen)
+ */
+static unsigned long max_frequency;
+
 static unsigned long long tsc_at_measure_start;
 static unsigned long long tsc_at_measure_end;
-static unsigned long max_frequency;
 static unsigned long long *mperf_previous_count;
 static unsigned long long *aperf_previous_count;
 static unsigned long long *mperf_current_count;
 static unsigned long long *aperf_current_count;
+
 /* valid flag for all CPUs. If a MSR read failed it will be zero */
 static int *is_valid;
 
 static int mperf_get_tsc(unsigned long long *tsc)
 {
-        return read_msr(0, MSR_TSC, tsc);
+        int ret;
+        ret = read_msr(0, MSR_TSC, tsc);
+        if (ret)
+                dprint("Reading TSC MSR failed, returning %llu\n", *tsc);
+        return ret;
 }
 
 static int mperf_init_stats(unsigned int cpu)
@@ -97,36 +114,11 @@ static int mperf_measure_stats(unsigned int cpu)
         return 0;
 }
 
-/*
- * get_average_perf()
- *
- * Returns the average performance (also considers boosted frequencies)
- *
- * Input:
- *   aperf_diff: Difference of the aperf register over a time period
- *   mperf_diff: Difference of the mperf register over the same time period
- *   max_freq:   Maximum frequency (P0)
- *
- * Returns:
- *   Average performance over the time period
- */
-static unsigned long get_average_perf(unsigned long long aperf_diff,
-                                      unsigned long long mperf_diff)
-{
-        unsigned int perf_percent = 0;
-        if (((unsigned long)(-1) / 100) < aperf_diff) {
-                int shift_count = 7;
-                aperf_diff >>= shift_count;
-                mperf_diff >>= shift_count;
-        }
-        perf_percent = (aperf_diff * 100) / mperf_diff;
-        return (max_frequency * perf_percent) / 100;
-}
-
 static int mperf_get_count_percent(unsigned int id, double *percent,
                                    unsigned int cpu)
 {
         unsigned long long aperf_diff, mperf_diff, tsc_diff;
+        unsigned long long timediff;
 
         if (!is_valid[cpu])
                 return -1;
@@ -136,11 +128,19 @@ static int mperf_get_count_percent(unsigned int id, double *percent,
 
         mperf_diff = mperf_current_count[cpu] - mperf_previous_count[cpu];
         aperf_diff = aperf_current_count[cpu] - aperf_previous_count[cpu];
-        tsc_diff = tsc_at_measure_end - tsc_at_measure_start;
 
-        *percent = 100.0 * mperf_diff / tsc_diff;
-        dprint("%s: mperf_diff: %llu, tsc_diff: %llu\n",
-               mperf_cstates[id].name, mperf_diff, tsc_diff);
+        if (max_freq_mode == MAX_FREQ_TSC_REF) {
+                tsc_diff = tsc_at_measure_end - tsc_at_measure_start;
+                *percent = 100.0 * mperf_diff / tsc_diff;
+                dprint("%s: TSC Ref - mperf_diff: %llu, tsc_diff: %llu\n",
+                       mperf_cstates[id].name, mperf_diff, tsc_diff);
+        } else if (max_freq_mode == MAX_FREQ_SYSFS) {
+                timediff = timespec_diff_us(time_start, time_end);
+                *percent = 100.0 * mperf_diff / timediff;
+                dprint("%s: MAXFREQ - mperf_diff: %llu, time_diff: %llu\n",
+                       mperf_cstates[id].name, mperf_diff, timediff);
+        } else
+                return -1;
 
         if (id == Cx)
                 *percent = 100.0 - *percent;
@@ -154,7 +154,7 @@ static int mperf_get_count_percent(unsigned int id, double *percent,
 static int mperf_get_count_freq(unsigned int id, unsigned long long *count,
                                 unsigned int cpu)
 {
-        unsigned long long aperf_diff, mperf_diff;
+        unsigned long long aperf_diff, mperf_diff, time_diff, tsc_diff;
 
         if (id != AVG_FREQ)
                 return 1;
@@ -165,11 +165,21 @@ static int mperf_get_count_freq(unsigned int id, unsigned long long *count,
         mperf_diff = mperf_current_count[cpu] - mperf_previous_count[cpu];
         aperf_diff = aperf_current_count[cpu] - aperf_previous_count[cpu];
 
-        /* Return MHz for now, might want to return KHz if column width is more
-           generic */
-        *count = get_average_perf(aperf_diff, mperf_diff) / 1000;
-        dprint("%s: %llu\n", mperf_cstates[id].name, *count);
+        if (max_freq_mode == MAX_FREQ_TSC_REF) {
+                /* Calculate max_freq from TSC count */
+                tsc_diff = tsc_at_measure_end - tsc_at_measure_start;
+                time_diff = timespec_diff_us(time_start, time_end);
+                max_frequency = tsc_diff / time_diff;
+        }
 
+        *count = max_frequency * ((double)aperf_diff / mperf_diff);
+        dprint("%s: Average freq based on %s maximum frequency:\n",
+               mperf_cstates[id].name,
+               (max_freq_mode == MAX_FREQ_TSC_REF) ? "TSC calculated" : "sysfs read");
+        dprint("%max_frequency: %lu", max_frequency);
+        dprint("aperf_diff: %llu\n", aperf_diff);
+        dprint("mperf_diff: %llu\n", mperf_diff);
+        dprint("avg freq:   %llu\n", *count);
         return 0;
 }
 
@@ -178,6 +188,7 @@ static int mperf_start(void)
         int cpu;
         unsigned long long dbg;
 
+        clock_gettime(CLOCK_REALTIME, &time_start);
         mperf_get_tsc(&tsc_at_measure_start);
 
         for (cpu = 0; cpu < cpu_count; cpu++)
@@ -193,32 +204,104 @@ static int mperf_stop(void)
         unsigned long long dbg;
         int cpu;
 
-        mperf_get_tsc(&tsc_at_measure_end);
-
         for (cpu = 0; cpu < cpu_count; cpu++)
                 mperf_measure_stats(cpu);
 
+        mperf_get_tsc(&tsc_at_measure_end);
+        clock_gettime(CLOCK_REALTIME, &time_end);
+
         mperf_get_tsc(&dbg);
         dprint("TSC diff: %llu\n", dbg - tsc_at_measure_end);
 
         return 0;
 }
 
-struct cpuidle_monitor mperf_monitor;
-
-struct cpuidle_monitor *mperf_register(void)
+/*
+ * Mperf register is defined to tick at P0 (maximum) frequency
+ *
+ * Instead of reading out P0 which can be tricky to read out from HW,
+ * we use TSC counter if it reliably ticks at P0/mperf frequency.
+ *
+ * Still try to fall back to:
+ * /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
+ * on older Intel HW without invariant TSC feature.
+ * Or on AMD machines where TSC does not tick at P0 (do not exist yet, but
+ * it's still double checked (MSR_AMD_HWCR)).
+ *
+ * On these machines the user would still get useful mperf
+ * stats when acpi-cpufreq driver is loaded.
+ */
+static int init_maxfreq_mode(void)
 {
+        int ret;
+        unsigned long long hwcr;
         unsigned long min;
 
-        if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_APERF))
-                return NULL;
-
-        /* Assume min/max all the same on all cores */
+        if (!cpupower_cpu_info.caps & CPUPOWER_CAP_INV_TSC)
+                goto use_sysfs;
+
+        if (cpupower_cpu_info.vendor == X86_VENDOR_AMD) {
+                /* MSR_AMD_HWCR tells us whether TSC runs at P0/mperf
+                 * freq.
+                 * A test whether hwcr is accessable/available would be:
+                 * (cpupower_cpu_info.family > 0x10 ||
+                 *   cpupower_cpu_info.family == 0x10 &&
+                 *   cpupower_cpu_info.model >= 0x2))
+                 * This should be the case for all aperf/mperf
+                 * capable AMD machines and is therefore safe to test here.
+                 * Compare with Linus kernel git commit: acf01734b1747b1ec4
+                 */
+                ret = read_msr(0, MSR_AMD_HWCR, &hwcr);
+                /*
+                 * If the MSR read failed, assume a Xen system that did
+                 * not explicitly provide access to it and assume TSC works
+                */
+                if (ret != 0) {
+                        dprint("TSC read 0x%x failed - assume TSC working\n",
+                               MSR_AMD_HWCR);
+                        return 0;
+                } else if (1 & (hwcr >> 24)) {
+                        max_freq_mode = MAX_FREQ_TSC_REF;
+                        return 0;
+                } else { /* Use sysfs max frequency if available */ }
+        } else if (cpupower_cpu_info.vendor == X86_VENDOR_INTEL) {
+                /*
+                 * On Intel we assume mperf (in C0) is ticking at same
+                 * rate than TSC
+                 */
+                max_freq_mode = MAX_FREQ_TSC_REF;
+                return 0;
+        }
+use_sysfs:
         if (cpufreq_get_hardware_limits(0, &min, &max_frequency)) {
                 dprint("Cannot retrieve max freq from cpufreq kernel "
                        "subsystem\n");
-                return NULL;
+                return -1;
         }
+        max_freq_mode = MAX_FREQ_SYSFS;
+        return 0;
+}
+
+/*
+ * This monitor provides:
+ *
+ * 1) Average frequency a CPU resided in
+ *    This always works if the CPU has aperf/mperf capabilities
+ *
+ * 2) C0 and Cx (any sleep state) time a CPU resided in
+ *    Works if mperf timer stops ticking in sleep states which
+ *    seem to be the case on all current HW.
+ * Both is directly retrieved from HW registers and is independent
+ * from kernel statistics.
+ */
+struct cpuidle_monitor mperf_monitor;
+struct cpuidle_monitor *mperf_register(void)
+{
+        if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_APERF))
+                return NULL;
+
+        if (init_maxfreq_mode())
+                return NULL;
 
         /* Free this at program termination */
         is_valid = calloc(cpu_count, sizeof(int));