Re: [PATCH v2 0/7] Share events between metrics

[kajoljain <kjain@linux.ibm.com>]

On 5/20/20 11:50 PM, Ian Rogers wrote:
> Metric groups contain metrics. Metrics create groups of events to
> ideally be scheduled together. Often metrics refer to the same events,
> for example, a cache hit and cache miss rate. Using separate event
> groups means these metrics are multiplexed at different times and the
> counts don't sum to 100%. More multiplexing also decreases the
> accuracy of the measurement.
> 
> This change orders metrics from groups or the command line, so that
> the ones with the most events are set up first. Later metrics see if
> groups already provide their events, and reuse them if
> possible. Unnecessary events and groups are eliminated.
> 
> The option --metric-no-group is added so that metrics aren't placed in
> groups. This affects multiplexing and may increase sharing.
> 
> The option --metric-mo-merge is added and with this option the
> existing grouping behavior is preserved.
> 
> Using skylakex metrics I ran the following shell code to count the
> number of events for each metric group (this ignores metric groups
> with a single metric, and one of the duplicated TopdownL1 and
> TopDownL1 groups):
> 
> for i in all Branches BrMispredicts Cache_Misses FLOPS Instruction_Type Memory_BW Pipeline Power SMT Summary TopdownL1 TopdownL1_SMT
> do
>   echo Metric group: $i
>   echo -n " - No merging (old default, now --metric-no-merge): "
>   /tmp/perf/perf stat -a --metric-no-merge -M $i sleep 1 2>&1 | grep -v "^ *#" | egrep " +[0-9,.]+ [^s]" | wc -l
>   echo -n " - Merging over metrics (new default)             : "
>   /tmp/perf/perf stat -a -M $i sleep 1 2>&1 | grep -v "^ *#" | egrep " +[0-9,.]+ [^s]"|wc -l
>   echo -n " - No event groups and merging (--metric-no-group): "
>   /tmp/perf/perf stat -a --metric-no-group -M $i sleep 1 2>&1 | grep -v "^ *#" | egrep " +[0-9,.]+ [^s]"|wc -l
> done
> 
> Metric group: all
>  - No merging (old default, now --metric-no-merge): 193
>  - Merging over metrics (new default)             : 142
>  - No event groups and merging (--metric-no-group): 84
> Metric group: Branches
>  - No merging (old default, now --metric-no-merge): 8
>  - Merging over metrics (new default)             : 8
>  - No event groups and merging (--metric-no-group): 4
> Metric group: BrMispredicts
>  - No merging (old default, now --metric-no-merge): 11
>  - Merging over metrics (new default)             : 11
>  - No event groups and merging (--metric-no-group): 10
> Metric group: Cache_Misses
>  - No merging (old default, now --metric-no-merge): 11
>  - Merging over metrics (new default)             : 9
>  - No event groups and merging (--metric-no-group): 6
> Metric group: FLOPS
>  - No merging (old default, now --metric-no-merge): 18
>  - Merging over metrics (new default)             : 10
>  - No event groups and merging (--metric-no-group): 10
> Metric group: Instruction_Type
>  - No merging (old default, now --metric-no-merge): 6
>  - Merging over metrics (new default)             : 6
>  - No event groups and merging (--metric-no-group): 4
> Metric group: Pipeline
>  - No merging (old default, now --metric-no-merge): 6
>  - Merging over metrics (new default)             : 6
>  - No event groups and merging (--metric-no-group): 5
> Metric group: Power
>  - No merging (old default, now --metric-no-merge): 16
>  - Merging over metrics (new default)             : 16
>  - No event groups and merging (--metric-no-group): 10
> Metric group: SMT
>  - No merging (old default, now --metric-no-merge): 11
>  - Merging over metrics (new default)             : 8
>  - No event groups and merging (--metric-no-group): 7
> Metric group: Summary
>  - No merging (old default, now --metric-no-merge): 19
>  - Merging over metrics (new default)             : 17
>  - No event groups and merging (--metric-no-group): 17
> Metric group: TopdownL1
>  - No merging (old default, now --metric-no-merge): 16
>  - Merging over metrics (new default)             : 7
>  - No event groups and merging (--metric-no-group): 7
> Metric group: TopdownL1_SMT
>  - No merging (old default, now --metric-no-merge): 24
>  - Merging over metrics (new default)             : 7
>  - No event groups and merging (--metric-no-group): 7
> 
> There are 5 out of 12 metric groups where no events are shared, such
> as Power, however, disabling grouping of events always reduces the
> number of events.
> 
> The result for Memory_BW needs explanation:
> 
> Metric group: Memory_BW
>  - No merging (old default, now --metric-no-merge): 9
>  - Merging over metrics (new default)             : 5
>  - No event groups and merging (--metric-no-group): 11
> 
> Both with and without merging the groups fail to be set up and so the
> event counts here are for broken metrics. The --metric-no-group number
> is accurate as all the events are scheduled. Ideally a constraint
> would be added for these metrics in the json code to avoid grouping.
> 
> v2. rebases on kernel/git/acme/linux.git branch tmp.perf/core, fixes a
> missing comma with metric lists (reported-by Jiri Olsa
> <jolsa@redhat.com>) and adds early returns to metricgroup__add_metric
> (suggested-by Jiri Olsa).
> 
> v1. was prepared on kernel/git/acme/linux.git branch tmp.perf/core
> 
> Compared to RFC v3: fix a bug where unnecessary commas were passed to
> parse-events and were echoed. Fix a bug where the same event could be
> matched more than once with --metric-no-group, causing there to be
> events missing.
> https://lore.kernel.org/lkml/20200508053629.210324-1-irogers@google.com/
> 
> Ian Rogers (7):
>   perf metricgroup: Always place duration_time last
>   perf metricgroup: Use early return in add_metric
>   perf metricgroup: Delay events string creation
>   perf metricgroup: Order event groups by size
>   perf metricgroup: Remove duped metric group events
>   perf metricgroup: Add options to not group or merge
>   perf metricgroup: Remove unnecessary ',' from events
> 

Reviewd-By: Kajol Jain <kjain@linux.ibm.com>
Tested-By: Kajol Jain <kjain@linux.ibm.com> ( Tested it to see behavior with some metric groups in both x86 and Power machine)

Thanks,
Kajol Jain

>  tools/perf/Documentation/perf-stat.txt |  19 ++
>  tools/perf/builtin-stat.c              |  11 +-
>  tools/perf/util/metricgroup.c          | 239 ++++++++++++++++++-------
>  tools/perf/util/metricgroup.h          |   6 +-
>  tools/perf/util/stat.h                 |   2 +
>  5 files changed, 207 insertions(+), 70 deletions(-)
>