Re: [PATCH 1/2] perf tests: Fix switch tracking test for P4

[Arnaldo Carvalho de Melo]

Em Fri, May 26, 2017 at 02:31:40PM +0200, Jiri Olsa escreveu:
> The switch tracking test keeps failing on P4 cpu,
> when NMI watchdog is enabled.
> 
> The reason is that P4 pmu uses substitute event for cycles
> when it's already taken (in our case by NMI watchdog), but
> this event does not give even results like cycles, and we
> could end up with no samples at all for our short
> measuring period.
> 
> Fixing this by using "instructions:u" event instead,
> which seems to be stable enough.

The original author of this test entry is Adrian, so would be nice for
him to take a look and give his Ack, Adrian?

- Arnaldo
 
> Cc: Michael Petlan <mpetlan@xxxxxxxxxx>
> Link: http://lkml.kernel.org/n/tip-4s8vo7skneszacdckv7uiog3@xxxxxxxxxxxxxx
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/perf/tests/switch-tracking.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/tests/switch-tracking.c b/tools/perf/tests/switch-tracking.c
> index 65474fd80da7..e519819ea2e5 100644
> --- a/tools/perf/tests/switch-tracking.c
> +++ b/tools/perf/tests/switch-tracking.c
> @@ -10,6 +10,7 @@
>  #include "thread_map.h"
>  #include "cpumap.h"
>  #include "tests.h"
> +#include "header.h"
>  
>  static int spin_sleep(void)
>  {
> @@ -298,6 +299,27 @@ static int process_events(struct perf_evlist *evlist,
>  	return ret;
>  }
>  
> +static const char *get_hw_counter(void)
> +{
> +	const char *counter = "cycles:u";
> +	char *cpuid;
> +
> +	cpuid = get_cpuid_str();
> +
> +	/*
> +	 * P4 pmu uses substitute event for cycles if it's already
> +	 * taken, but it does not give even results like cycles,
> +	 * and we could end up with no samples at all for our short
> +	 * measuring period. Using "instructions:u" event instead,
> +	 * which seems to be stable enough.
> +	 */
> +	if (!strcmp("GenuineIntel-15-4", cpuid))
> +		counter = "instructions:u";
> +
> +	pr_debug("using '%s' HW counter");
> +	return counter;
> +}
> +
>  /**
>   * test__switch_tracking - test using sched_switch and tracking events.
>   *
> @@ -308,6 +330,7 @@ static int process_events(struct perf_evlist *evlist,
>   */
>  int test__switch_tracking(int subtest __maybe_unused)
>  {
> +	const char *hw_counter = get_hw_counter();
>  	const char *sched_switch = "sched:sched_switch";
>  	struct switch_tracking switch_tracking = { .tids = NULL, };
>  	struct record_opts opts = {
> @@ -357,9 +380,9 @@ int test__switch_tracking(int subtest __maybe_unused)
>  	cpu_clocks_evsel = perf_evlist__last(evlist);
>  
>  	/* Second event */
> -	err = parse_events(evlist, "cycles:u", NULL);
> +	err = parse_events(evlist, hw_counter, NULL);
>  	if (err) {
> -		pr_debug("Failed to parse event cycles:u\n");
> +		pr_debug("Failed to parse event %s\n", hw_counter);
>  		goto out_err;
>  	}
>  
> -- 
> 2.9.4