perf tools: Fix SMT fallback with large core counts

strtoull can only read a 64-bit bitmap. On an AMD EPYC core_cpus may look
like:

00000000,00000000,00000000,00000001,00000000,00000000,00000000,00000001

and so the sibling wasn't spotted. Fix by writing a simple hweight string
parser.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211124001231.3277836-3-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 34f1b1b..2636be6 100644 (file)
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -5,6 +5,56 @@
 #include "api/fs/fs.h"
 #include "smt.h"
 
+/**
+ * hweight_str - Returns the number of bits set in str. Stops at first non-hex
+ *            or ',' character.
+ */
+static int hweight_str(char *str)
+{
+       int result = 0;
+
+       while (*str) {
+               switch (*str++) {
+               case '0':
+               case ',':
+                       break;
+               case '1':
+               case '2':
+               case '4':
+               case '8':
+                       result++;
+                       break;
+               case '3':
+               case '5':
+               case '6':
+               case '9':
+               case 'a':
+               case 'A':
+               case 'c':
+               case 'C':
+                       result += 2;
+                       break;
+               case '7':
+               case 'b':
+               case 'B':
+               case 'd':
+               case 'D':
+               case 'e':
+               case 'E':
+                       result += 3;
+                       break;
+               case 'f':
+               case 'F':
+                       result += 4;
+                       break;
+               default:
+                       goto done;
+               }
+       }
+done:
+       return result;
+}
+
 int smt_on(void)
 {
        static bool cached;
@@ -15,9 +65,12 @@ int smt_on(void)
        if (cached)
                return cached_result;
 
-       if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0)
-               goto done;
+       if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {
+               cached = true;
+               return cached_result;
+       }
 
+       cached_result = 0;
        ncpu = sysconf(_SC_NPROCESSORS_CONF);
        for (cpu = 0; cpu < ncpu; cpu++) {
                unsigned long long siblings;
@@ -35,18 +88,13 @@ int smt_on(void)
                                continue;
                }
                /* Entry is hex, but does not have 0x, so need custom parser */
-               siblings = strtoull(str, NULL, 16);
+               siblings = hweight_str(str);
                free(str);
-               if (hweight64(siblings) > 1) {
+               if (siblings > 1) {
                        cached_result = 1;
-                       cached = true;
                        break;
                }
        }
-       if (!cached) {
-               cached_result = 0;
-done:
-               cached = true;
-       }
+       cached = true;
        return cached_result;
 }