On Wed, 7 Jul 2021, Nicolas Saenz Julienne wrote:
> The point of preheat is to make sure CPUs are out of idle and running at
> max frequency by the time the real test starts. So it's expected to
> incur into extra latencies we don't really mean to measure. With this in
> mind, it doesn't make sense to take into account the trace threshold
> during that run. So don't do it.
>
> Note that this has been observed in practice. The threshold would be hit
> during preheat but not during the real test.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
> ---
> src/oslat/oslat.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/src/oslat/oslat.c b/src/oslat/oslat.c
> index 1cba6fc..6ff5ba8 100644
> --- a/src/oslat/oslat.c
> +++ b/src/oslat/oslat.c
> @@ -29,6 +29,7 @@
> #include <numa.h>
> #include <math.h>
> #include <limits.h>
> +#include <stdbool.h>
>
> #include <sys/prctl.h>
> #include <sys/stat.h>
> @@ -150,6 +151,7 @@ struct thread {
> struct global {
> /* Configuration. */
> unsigned int runtime_secs;
> + bool preheat;
> /*
> * Number of threads running for current test
> * (either pre heat or real run)
> @@ -299,7 +301,7 @@ static void insert_bucket(struct thread *t, stamp_t value)
> us = index + 1;
> assert(us > 0);
>
> - if (g.trace_threshold && us >= g.trace_threshold) {
> + if (!g.preheat && g.trace_threshold && us >= g.trace_threshold) {
> char *line = "%s: Trace threshold (%d us) triggered with %u us!\n"
> "Stopping the test.\n";
> tracemark(line, g.app_name, g.trace_threshold, us);
> @@ -515,11 +517,12 @@ static void write_summary_json(FILE *f, void *data)
> fprintf(f, " }\n");
> }
>
> -static void run_expt(struct thread *threads, int runtime_secs)
> +static void run_expt(struct thread *threads, int runtime_secs, bool preheat)
> {
> int i;
>
> g.runtime_secs = runtime_secs;
> + g.preheat = preheat;
> g.n_threads_started = 0;
> g.n_threads_running = 0;
> g.n_threads_finished = 0;
> @@ -846,14 +849,14 @@ int main(int argc, char *argv[])
> g.n_threads = 1;
> else
> g.n_threads = g.n_threads_total;
> - run_expt(threads, 1);
> + run_expt(threads, 1, true);
> record_bias(threads);
>
> if (!g.quiet)
> printf("Test starts...\n");
> /* Reset n_threads to always run on all the cores */
> g.n_threads = g.n_threads_total;
> - run_expt(threads, g.runtime);
> + run_expt(threads, g.runtime, false);
>
> if (!g.quiet)
> printf("Test completed.\n\n");
> --
> 2.31.1
>
>
Signed-off-by: John Kacur <jkacur@xxxxxxxxxx>
