perf tools: No need to unconditionally read the max_stack sysctls

Let tools that need to have those variables with the sysctl current
values use a function that will read them.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-1ljj3oeo5kpt2n1icfd9vowe@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -1264,7 +1264,7 @@ int cmd_top(int argc, const char **argv)
 			.proc_map_timeout    = 500,
 			.overwrite	= 1,
 		},
-		.max_stack	     = sysctl_perf_event_max_stack,
+		.max_stack	     = sysctl__max_stack(),
 		.sym_pcnt_filter     = 5,
 		.nr_threads_synthesize = UINT_MAX,
 	};

tools/perf/builtin-trace.c

@@ -3162,7 +3162,7 @@ int cmd_trace(int argc, const char **argv)
 		mmap_pages_user_set = false;
 
 	if (trace.max_stack == UINT_MAX) {
-		trace.max_stack = input_name ? PERF_MAX_STACK_DEPTH : sysctl_perf_event_max_stack;
+		trace.max_stack = input_name ? PERF_MAX_STACK_DEPTH : sysctl__max_stack();
 		max_stack_user_set = false;
 	}
 

tools/perf/perf.c

@@ -426,7 +426,6 @@ int main(int argc, const char **argv)
 	int err;
 	const char *cmd;
 	char sbuf[STRERR_BUFSIZE];
-	int value;
 
 	/* libsubcmd init */
 	exec_cmd_init("perf", PREFIX, PERF_EXEC_PATH, EXEC_PATH_ENVIRONMENT);
@@ -435,12 +434,6 @@ int main(int argc, const char **argv)
 	/* The page_size is placed in util object. */
 	page_size = sysconf(_SC_PAGE_SIZE);
 
-	if (sysctl__read_int("kernel/perf_event_max_stack", &value) == 0)
-		sysctl_perf_event_max_stack = value;
-
-	if (sysctl__read_int("kernel/perf_event_max_contexts_per_stack", &value) == 0)
-		sysctl_perf_event_max_contexts_per_stack = value;
-
 	cmd = extract_argv0_path(argv[0]);
 	if (!cmd)
 		cmd = "perf-help";

tools/perf/util/evsel.c

@@ -2862,7 +2862,7 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 			return scnprintf(msg, size,
 					 "Not enough memory to setup event with callchain.\n"
 					 "Hint: Try tweaking /proc/sys/kernel/perf_event_max_stack\n"
-					 "Hint: Current value: %d", sysctl_perf_event_max_stack);
+					 "Hint: Current value: %d", sysctl__max_stack());
 		break;
 	case ENODEV:
 		if (target->cpu_list)

tools/perf/util/util.c

@@ -62,6 +62,19 @@ int cacheline_size(void)
 int sysctl_perf_event_max_stack = PERF_MAX_STACK_DEPTH;
 int sysctl_perf_event_max_contexts_per_stack = PERF_MAX_CONTEXTS_PER_STACK;
 
+int sysctl__max_stack(void)
+{
+	int value;
+
+	if (sysctl__read_int("kernel/perf_event_max_stack", &value) == 0)
+		sysctl_perf_event_max_stack = value;
+
+	if (sysctl__read_int("kernel/perf_event_max_contexts_per_stack", &value) == 0)
+		sysctl_perf_event_max_contexts_per_stack = value;
+
+	return sysctl_perf_event_max_stack;
+}
+
 bool test_attr__enabled;
 
 bool perf_host  = true;

tools/perf/util/util.h

@@ -45,6 +45,8 @@ int hex2u64(const char *ptr, u64 *val);
 extern unsigned int page_size;
 int __pure cacheline_size(void);
 
+int sysctl__max_stack(void);
+
 int fetch_kernel_version(unsigned int *puint,
 			 char *str, size_t str_sz);
 #define KVER_VERSION(x)		(((x) >> 16) & 0xff)