'cpu_mhz' in oslat actually represents the frequency at which the high
frequency counter we measure with ticks. There is no requirement for the
counter to match the CPU frequency, nor is forced to do so on any of the
supported architectures[1][2]. So rename it to 'counter_mhz' in order to
better match reality.
[1] x86_64
Intel TRM Vol 3B, 17.17 Time Stamp Counter:
"Constant TSC behavior ensures that the duration of each clock tick is
uniform and supports the use of the TSC as a wall clock timer even if
the processor core changes frequency."
[2] ppc64
>From __ppc_get_timebase() manpages: The Time Base Register is a 64-bit
register provided by Power Architecture processors. It stores a
monotonically incremented value that is updated at a system-dependent
frequency that may be different from the processor frequency. Note that
glibc's __ppc_get_timebase() and oslat's ppc64 frc() implementations are
the same.
Signed-off-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
---
Changes since v1:
- More complete commit message
- s/timer/counter/
src/oslat/oslat.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/src/oslat/oslat.c b/src/oslat/oslat.c
index 6ff5ba8..33cccd3 100644
--- a/src/oslat/oslat.c
+++ b/src/oslat/oslat.c
@@ -123,7 +123,7 @@ struct thread {
pthread_t thread_id;
/* NOTE! this is also how many ticks per us */
- unsigned int cpu_mhz;
+ unsigned int counter_mhz;
cycles_t int_total;
stamp_t frc_start;
stamp_t frc_stop;
@@ -228,7 +228,7 @@ static int move_to_core(int core_i)
return sched_setaffinity(0, sizeof(cpus), &cpus);
}
-static cycles_t __measure_cpu_hz(void)
+static cycles_t __measure_counter_hz(void)
{
struct timeval tvs, tve;
stamp_t s, e;
@@ -244,13 +244,13 @@ static cycles_t __measure_cpu_hz(void)
return (cycles_t) ((e - s) / sec);
}
-static unsigned int measure_cpu_mhz(void)
+static unsigned int measure_counter_mhz(void)
{
cycles_t m, mprev, d;
- mprev = __measure_cpu_hz();
+ mprev = __measure_counter_hz();
do {
- m = __measure_cpu_hz();
+ m = __measure_counter_hz();
if (m > mprev)
d = m - mprev;
else
@@ -263,7 +263,7 @@ static unsigned int measure_cpu_mhz(void)
static void thread_init(struct thread *t)
{
- t->cpu_mhz = measure_cpu_mhz();
+ t->counter_mhz = measure_counter_mhz();
t->maxlat = 0;
t->overflow_sum = 0;
t->minlat = (uint64_t)-1;
@@ -288,7 +288,7 @@ static void thread_init(struct thread *t)
static float cycles_to_sec(const struct thread *t, uint64_t cycles)
{
- return cycles / (t->cpu_mhz * 1e6);
+ return cycles / (t->counter_mhz * 1e6);
}
static void insert_bucket(struct thread *t, stamp_t value)
@@ -296,7 +296,7 @@ static void insert_bucket(struct thread *t, stamp_t value)
int index, us;
uint64_t extra;
- index = value / t->cpu_mhz;
+ index = value / t->counter_mhz;
assert(index >= 0);
us = index + 1;
assert(us > 0);
@@ -450,7 +450,7 @@ static void write_summary(struct thread *t)
calculate(t);
putfield("Core", t[i].core_i, "d", "");
- putfield("CPU Freq", t[i].cpu_mhz, "u", " (Mhz)");
+ putfield("Counter Freq", t[i].counter_mhz, "u", " (Mhz)");
for (j = 0; j < g.bucket_size; j++) {
if (j < g.bucket_size-1 && g.output_omit_zero_buckets) {
@@ -494,7 +494,7 @@ static void write_summary_json(FILE *f, void *data)
for (i = 0; i < g.n_threads; ++i) {
fprintf(f, " \"%u\": {\n", i);
fprintf(f, " \"cpu\": %d,\n", t[i].core_i);
- fprintf(f, " \"freq\": %d,\n", t[i].cpu_mhz);
+ fprintf(f, " \"freq\": %d,\n", t[i].counter_mhz);
fprintf(f, " \"min\": %" PRIu64 ",\n", t[i].minlat);
fprintf(f, " \"avg\": %3lf,\n", t[i].average);
fprintf(f, " \"max\": %" PRIu64 ",\n", t[i].maxlat);
--
2.31.1
