perf tools: Fix reading new topology attribute "core_cpus"

Check if access("devices/system/cpu/cpu%d/topology/core_cpus", F_OK)
fails, which will happen unless the current directory is "/sys".

Simply try to read this file first.

Fixes: 0ccdb8407a46 ("perf tools: Apply new CPU topology sysfs attributes")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/158817718710.747528.11009278875028211991.stgit@buzz
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 3b791ef..8481842 100644 (file)
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -24,13 +24,13 @@ int smt_on(void)
 
                snprintf(fn, sizeof fn,
                        "devices/system/cpu/cpu%d/topology/core_cpus", cpu);
-               if (access(fn, F_OK) == -1) {
+               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;
                }
-               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);