[PATCH 38/91] perf tools: Simplify checking if SMT is active.

Arnaldo Carvalho de Melo
2020-05-06T15:25:11Z

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

SMT now could be disabled via "/sys/devices/system/cpu/smt/control".

Status is shown in "/sys/devices/system/cpu/smt/active" simply as "0" / "1".

If this knob isn't here then fallback to checking topology as before.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/158817741394.748034.9273604089138009552.stgit@buzz
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/smt.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 8481842e9edb..20bacd5972ad 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -15,6 +15,9 @@ int smt_on(void)
if (cached)
return cached_result;

+ if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) > 0)
+ goto done;
+
ncpu = sysconf(_SC_NPROCESSORS_CONF);
for (cpu = 0; cpu < ncpu; cpu++) {
unsigned long long siblings;
@@ -42,6 +45,7 @@ int smt_on(void)
}
if (!cached) {
cached_result = 0;
+done:
cached = true;
}
return cached_result;
--
2.21.1