On Mon, 13 Sep 2021, Nicolas Saenz Julienne wrote:
> '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
>
>
Waiting for a Signed-off-by: from Peter Xu before I integrate these.
Thanks
John
