[tip:perf/core] perf tools: Add utility function to detect SMT status

[tip-bot for Andi Kleen <tipbot@zytor.com>]

Commit-ID:  de5077c4e38f2a51f50d28bdd5e4a0f14b3d16ff
Gitweb:     http://git.kernel.org/tip/de5077c4e38f2a51f50d28bdd5e4a0f14b3d16ff
Author:     Andi Kleen <ak@linux.intel.com>
AuthorDate: Fri, 11 Aug 2017 16:26:22 -0700
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 22 Aug 2017 12:09:04 -0300

perf tools: Add utility function to detect SMT status

Add an smt_on() function to return if SMT is enabled or disabled.  Used
in the next patch.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170811232634.30465-7-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/Build |  1 +
 tools/perf/util/smt.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/smt.h |  6 ++++++
 3 files changed, 51 insertions(+)

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 8d49a98..94518c1 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -22,6 +22,7 @@ libperf-y += rbtree.o
 libperf-y += libstring.o
 libperf-y += bitmap.o
 libperf-y += hweight.o
+libperf-y += smt.o
 libperf-y += quote.o
 libperf-y += strbuf.o
 libperf-y += string.o
diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
new file mode 100644
index 0000000..453f6f6
--- /dev/null
+++ b/tools/perf/util/smt.c
@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <linux/bitops.h>
+#include "api/fs/fs.h"
+#include "smt.h"
+
+int smt_on(void)
+{
+	static bool cached;
+	static int cached_result;
+	int cpu;
+	int ncpu;
+
+	if (cached)
+		return cached_result;
+
+	ncpu = sysconf(_SC_NPROCESSORS_CONF);
+	for (cpu = 0; cpu < ncpu; cpu++) {
+		unsigned long long siblings;
+		char *str;
+		size_t strlen;
+		char fn[256];
+
+		snprintf(fn, sizeof fn,
+			"devices/system/cpu/cpu%d/topology/thread_siblings",
+			cpu);
+		if (sysfs__read_str(fn, &str, &strlen) < 0)
+			continue;
+		/* Entry is hex, but does not have 0x, so need custom parser */
+		siblings = strtoull(str, NULL, 16);
+		free(str);
+		if (hweight64(siblings) > 1) {
+			cached_result = 1;
+			cached = true;
+			break;
+		}
+	}
+	if (!cached) {
+		cached_result = 0;
+		cached = true;
+	}
+	return cached_result;
+}
diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
new file mode 100644
index 0000000..b8414b7
--- /dev/null
+++ b/tools/perf/util/smt.h
@@ -0,0 +1,6 @@
+#ifndef SMT_H
+#define SMT_H 1
+
+int smt_on(void);
+
+#endif