[PATCH v3] perf tools: fix detecting SMT at machines with more than 32 cpus

[Konstantin Khlebnikov]

Cpu bitmap is split into 32 bit words. For system with more than 32 cores
threads are always in different words thus first word never has two bits:
cpu0: "0000,00000100,00000001", cpu 79: "8000,00000080,00000000".

Instead of parsing bitmap read "core_cpus_list" or "thread_siblings_list"
and simply check presence of ',' or '-' in it.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Fixes: de5077c4e38f ("perf tools: Add utility function to detect SMT status")
---
 tools/perf/util/smt.c |   39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 20bacd5972ad..ef713981725a 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <string.h>
 #include <linux/bitops.h>
 #include "api/fs/fs.h"
 #include "smt.h"
@@ -9,6 +10,7 @@ int smt_on(void)
 {
 	static bool cached;
 	static int cached_result;
+	char *str = NULL;
 	int cpu;
 	int ncpu;
 
@@ -20,33 +22,24 @@ int smt_on(void)
 
 	ncpu = sysconf(_SC_NPROCESSORS_CONF);
 	for (cpu = 0; cpu < ncpu; cpu++) {
-		unsigned long long siblings;
-		char *str;
-		size_t strlen;
 		char fn[256];
+		size_t len;
 
-		snprintf(fn, sizeof fn,
-			"devices/system/cpu/cpu%d/topology/core_cpus", cpu);
-		if (sysfs__read_str(fn, &str, &strlen) < 0) {
-			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;
+		snprintf(fn, sizeof(fn), "devices/system/cpu/cpu%d/topology/%s",
+			 cpu, "core_cpus_list");
+		if (sysfs__read_str(fn, &str, &len) > 0)
+			break;
+
+		snprintf(fn, sizeof(fn), "devices/system/cpu/cpu%d/topology/%s",
+			 cpu, "thread_siblings_list");
+		if (sysfs__read_str(fn, &str, &len) > 0)
 			break;
-		}
 	}
-	if (!cached) {
-		cached_result = 0;
+
+	// ',' or '-' should be in string if list contains more than one cpu
+	cached_result = str && (strchr(str, ',') || strchr(str, '-'));
+	free(str);
 done:
-		cached = true;
-	}
+	cached = true;
 	return cached_result;
 }