Re: [PATCH v3 3/4] perf record: Don't clear event's period if set by a term

Adrian Hunter
2020-09-14T06:03:07Z

On 12/09/20 5:56 am, Ian Rogers wrote:
> If events in a group explicitly set a frequency or period with leader
> sampling, don't disable the samples on those events.
>
> Prior to 5.8:
> perf record -e '{cycles/period=12345000/,instructions/period=6789000/}:S'
> would clear the attributes then apply the config terms. In commit
> 5f34278867b7 leader sampling configuration was moved to after applying the
> config terms, in the example, making the instructions' event have its period
> cleared.
> This change makes it so that sampling is only disabled if configuration
> terms aren't present.
>
> Fixes: 5f34278867b7 ("perf evlist: Move leader-sampling configuration")
> Signed-off-by: Ian Rogers <irogers@google.com>

Acked-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
> tools/perf/util/record.c | 34 ++++++++++++++++++++++++++--------
> 1 file changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
> index a4cc11592f6b..ea9aa1d7cf50 100644
> --- a/tools/perf/util/record.c
> +++ b/tools/perf/util/record.c
> @@ -2,6 +2,7 @@
> #include "debug.h"
> #include "evlist.h"
> #include "evsel.h"
> +#include "evsel_config.h"
> #include "parse-events.h"
> #include <errno.h>
> #include <limits.h>
> @@ -33,11 +34,24 @@ static struct evsel *evsel__read_sampler(struct evsel *evsel, struct evlist *evl
> return leader;
> }
>
> +static u64 evsel__config_term_mask(struct evsel *evsel)
> +{
> + struct evsel_config_term *term;
> + struct list_head *config_terms = &evsel->config_terms;
> + u64 term_types = 0;
> +
> + list_for_each_entry(term, config_terms, list) {
> + term_types |= 1 << term->type;
> + }
> + return term_types;
> +}
> +
> static void evsel__config_leader_sampling(struct evsel *evsel, struct evlist *evlist)
> {
> struct perf_event_attr *attr = &evsel->core.attr;
> struct evsel *leader = evsel->leader;
> struct evsel *read_sampler;
> + u64 term_types, freq_mask;
>
> if (!leader->sample_read)
> return;
> @@ -47,16 +61,20 @@ static void evsel__config_leader_sampling(struct evsel *evsel, struct evlist *ev
> if (evsel == read_sampler)
> return;
>
> + term_types = evsel__config_term_mask(evsel);
> /*
> - * Disable sampling for all group members other than the leader in
> - * case the leader 'leads' the sampling, except when the leader is an
> - * AUX area event, in which case the 2nd event in the group is the one
> - * that 'leads' the sampling.
> + * Disable sampling for all group members except those with explicit
> + * config terms or the leader. In the case of an AUX area event, the 2nd
> + * event in the group is the one that 'leads' the sampling.
> */
> - attr->freq = 0;
> - attr->sample_freq = 0;
> - attr->sample_period = 0;
> - attr->write_backward = 0;
> + freq_mask = (1 << EVSEL__CONFIG_TERM_FREQ) | (1 << EVSEL__CONFIG_TERM_PERIOD);
> + if ((term_types & freq_mask) == 0) {
> + attr->freq = 0;
> + attr->sample_freq = 0;
> + attr->sample_period = 0;
> + }
> + if ((term_types & (1 << EVSEL__CONFIG_TERM_OVERWRITE)) == 0)
> + attr->write_backward = 0;
>
> /*
> * We don't get a sample for slave events, we make them when delivering
>