The evlist__for_each_cpu iterator will call sched_setaffitinity when
moving between CPUs to avoid IPIs.
If only 1 IPI is saved then this may be unprofitable as the delay to get
scheduled may be considerable.
This may be particularly true if reading an event group in `perf stat`
in interval mode.
Move the affinity handling completely into the iterator so that a single
evlist__use_affinity can determine whether CPU affinities will be used.
For `perf record` the change is minimal as the dummy event and the real
event will always make the use of affinities the thing to do.
In `perf stat`, tool events are ignored and affinities only used if >1
event on the same CPU occur.
Determining if affinities are useful is done by evlist__use_affinity
which tests per-event whether the event's PMU benefits from affinity use
- it is assumed only perf event using PMUs do.
Fix a bug where when there are no affinities that the CPU map iterator
may reference a CPU not present in the initial evsel. Fix by making the
iterator and non-iterator code common.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
d484361550