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Subject[PATCH v3] perf tools: fix detecting SMT at machines with more than 32 cpus
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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@yandex-team.ru>
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;
}
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