linux-kernel - [PATCH v2 3/3] perf tool: simplify checking active smt

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Message-ID: <158817741394.748034.9273604089138009552.stgit@buzz>
Date:   Wed, 29 Apr 2020 19:23:41 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: [PATCH v2 3/3] perf tool: simplify checking active smt

SMT now could be disabled via "/sys/devices/system/cpu/smt/control".
Status 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@...dex-team.ru>
---
 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 dc37b5abd1c3..c398528d1006 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -19,6 +19,9 @@ int smt_on(void)
 	if (cached)
 		return cached_result;
 
+	if (sysfs__read_int("devices/system/cpu/smt/active", &active) > 0)
+		goto done;
+
 	ncpu = sysconf(_SC_NPROCESSORS_CONF);
 	for (cpu = 0; cpu < ncpu; cpu++) {
 		char fn[256];
@@ -37,6 +40,7 @@ int smt_on(void)
 	active = str && (strchr(str, ',') != NULL || strchr(str, '-') != NULL);
 	free(str);
 
+done:
 	if (!cached) {
 		cached_result = active;
 		cached = true;