[PATCH v2 1/3] perf tool: fix reading new topology attribute "core_cpus"

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: linux-kernel@vger.kernel.org,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Andi Kleen <ak@linux.intel.com>,
	Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Subject: [PATCH v2 1/3] perf tool: fix reading new topology attribute "core_cpus"
Date: Wed, 29 Apr 2020 19:19:47 +0300	[thread overview]
Message-ID: <158817718710.747528.11009278875028211991.stgit@buzz> (raw)

Check access("devices/system/cpu/cpu%d/topology/core_cpus", F_OK) fails,
unless current directory is "/sys". Simply try read this file first.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: 0ccdb8407a46 ("perf tools: Apply new CPU topology sysfs attributes")
---
 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 3b791ef2cd50..8481842e9edb 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);

