[tip: perf/core] perf tools: Fix reading new topology attribute "core_cpus"

[tip-bot2 for Konstantin Khlebnikov]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     846de4371fdfddfa49481e3d04884539870dc127
Gitweb:        https://git.kernel.org/tip/846de4371fdfddfa49481e3d04884539870dc127
Author:        Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
AuthorDate:    Wed, 29 Apr 2020 19:19:47 +03:00
Committer:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitterDate: Tue, 05 May 2020 16:35:29 -03:00

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@xxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lore.kernel.org/lkml/158817718710.747528.11009278875028211991.stgit@buzz
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/smt.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 3b791ef..8481842 100644
--- 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);