linux-kernel - [PATCH v2 2/3] perf tool: fix detecting smt at machines with more than 32 cpus

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Message-ID: <158817735893.747933.15107805593224835078.stgit@buzz>
Date:   Wed, 29 Apr 2020 19:22:43 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: [PATCH v2 2/3] perf tool: fix detecting smt at machines with more
 than 32 cpus

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@...dex-team.ru>
Fixes: de5077c4e38f ("perf tools: Add utility function to detect SMT status")
---
 tools/perf/util/smt.c |   37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 8481842e9edb..dc37b5abd1c3 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"
@@ -9,39 +10,35 @@ int smt_on(void)
 {
 	static bool cached;
 	static int cached_result;
+	int active;
 	int cpu;
 	int ncpu;
+	char *str = NULL;
+	size_t strlen;
 
 	if (cached)
 		return cached_result;
 
 	ncpu = sysconf(_SC_NPROCESSORS_CONF);
 	for (cpu = 0; cpu < ncpu; cpu++) {
-		unsigned long long siblings;
-		char *str;
-		size_t strlen;
 		char fn[256];
 
-		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, &strlen) > 0)
+			break;
+
+		snprintf(fn, sizeof(fn), "devices/system/cpu/cpu%d/topology/%s",
+			 cpu, "thread_siblings_list");
+		if (sysfs__read_str(fn, &str, &strlen) > 0)
 			break;
-		}
 	}
+
+	active = str && (strchr(str, ',') != NULL || strchr(str, '-') != NULL);
+	free(str);
+
 	if (!cached) {
-		cached_result = 0;
+		cached_result = active;
 		cached = true;
 	}
 	return cached_result;