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>

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 8d49a989f1932f838543b90fb66ebd7b90481d95..94518c1bf8b6c37896c8f90430c4056012f6b29e 100644 (file)
--- 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 (file)
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 (file)
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