[tip: perf/core] perf tools: Simplify checking if SMT is active.

[tip-bot2 for Konstantin Khlebnikov]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     bb629484d924118e3b1d8652177040115adcba01
Gitweb:        https://git.kernel.org/tip/bb629484d924118e3b1d8652177040115adcba01
Author:        Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
AuthorDate:    Wed, 29 Apr 2020 19:23:41 +03:00
Committer:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitterDate: Tue, 05 May 2020 16:35:29 -03:00

perf tools: Simplify checking if SMT is active.

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@xxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lore.kernel.org/lkml/158817741394.748034.9273604089138009552.stgit@buzz
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 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 8481842..20bacd5 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;