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Subject[PATCH 2/3] perf tools: Fix SMT not detected with large core count
From
sysfs__read_int returns 0 on success, and so the fast read path was
always failing.
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.

Fixes: bb629484d924 (perf tools: Simplify checking if SMT is active.)
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/smt.c | 68 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 58 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 20bacd5972ad..2636be65305a 100644
--- 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;
}
--
2.34.0.rc2.393.gf8c9666880-goog
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