Messages in this thread Patch in this message | | | Date | Tue, 23 Nov 2021 14:48:20 -0800 | Subject | [PATCH 2/3] perf tools: Fix SMT not detected with large core count | From | Ian Rogers <> |
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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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