perf smt: Compute SMT from topology

The topology records sibling threads. Rather than computing SMT using
siblings in sysfs, reuse the values in topology. This only applies
when the file smt/active isn't available.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Ahmad Yasin <ahmad.yasin@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kshipra Bopardikar <kshipra.bopardikar@intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Miaoqian Lin <linmq006@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20220831174926.579643-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/expr.c

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#include "util/cputopo.h"
 #include "util/debug.h"
 #include "util/expr.h"
 #include "util/header.h"
@@ -154,15 +155,20 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
 						    (void **)&val_ptr));
 
 	/* Only EVENT1 or EVENT2 need be measured depending on the value of smt_on. */
-	expr__ctx_clear(ctx);
+	{
-	TEST_ASSERT_VAL("find ids",
+		struct cpu_topology *topology = cpu_topology__new();
-			expr__find_ids("EVENT1 if #smt_on else EVENT2",
+		bool smton = smt_on(topology);
-				NULL, ctx) == 0);
-	TEST_ASSERT_VAL("find ids", hashmap__size(ctx->ids) == 1);
-	TEST_ASSERT_VAL("find ids", hashmap__find(ctx->ids,
-						  smt_on() ? "EVENT1" : "EVENT2",
-						  (void **)&val_ptr));
 
+		cpu_topology__delete(topology);
+		expr__ctx_clear(ctx);
+		TEST_ASSERT_VAL("find ids",
+				expr__find_ids("EVENT1 if #smt_on else EVENT2",
+					NULL, ctx) == 0);
+		TEST_ASSERT_VAL("find ids", hashmap__size(ctx->ids) == 1);
+		TEST_ASSERT_VAL("find ids", hashmap__find(ctx->ids,
+							  smton ? "EVENT1" : "EVENT2",
+							  (void **)&val_ptr));
+	}
 	/* The expression is a constant 1.0 without needing to evaluate EVENT1. */
 	expr__ctx_clear(ctx);
 	TEST_ASSERT_VAL("find ids",

tools/perf/util/cputopo.c

@@ -157,6 +157,21 @@ void cpu_topology__delete(struct cpu_topology *tp)
 	free(tp);
 }
 
+bool cpu_topology__smt_on(const struct cpu_topology *topology)
+{
+	for (u32 i = 0; i < topology->core_cpus_lists; i++) {
+		const char *cpu_list = topology->core_cpus_list[i];
+
+		/*
+		 * If there is a need to separate siblings in a core then SMT is
+		 * enabled.
+		 */
+		if (strchr(cpu_list, ',') || strchr(cpu_list, '-'))
+			return true;
+	}
+	return false;
+}
+
 static bool has_die_topology(void)
 {
 	char filename[MAXPATHLEN];

tools/perf/util/cputopo.h

@@ -58,6 +58,8 @@ struct hybrid_topology {
 
 struct cpu_topology *cpu_topology__new(void);
 void cpu_topology__delete(struct cpu_topology *tp);
+/* Determine from the core list whether SMT was enabled. */
+bool cpu_topology__smt_on(const struct cpu_topology *topology);
 
 struct numa_topology *numa_topology__new(void);
 void numa_topology__delete(struct numa_topology *tp);

tools/perf/util/expr.c

@@ -412,11 +412,6 @@ double expr__get_literal(const char *literal)
 	static struct cpu_topology *topology;
 	double result = NAN;
 
-	if (!strcasecmp("#smt_on", literal)) {
-		result = smt_on() > 0 ? 1.0 : 0.0;
-		goto out;
-	}
-
 	if (!strcmp("#num_cpus", literal)) {
 		result = cpu__max_present_cpu().cpu;
 		goto out;
@@ -440,6 +435,10 @@ double expr__get_literal(const char *literal)
 			goto out;
 		}
 	}
+	if (!strcasecmp("#smt_on", literal)) {
+		result = smt_on(topology) ? 1.0 : 0.0;
+		goto out;
+	}
 	if (!strcmp("#num_packages", literal)) {
 		result = topology->package_cpus_lists;
 		goto out;

tools/perf/util/smt.c

@@ -1,100 +1,23 @@
 // SPDX-License-Identifier: GPL-2.0-only
-#include <stdio.h>
+#include <string.h>
-#include <stdlib.h>
-#include <unistd.h>
-#include <linux/bitops.h>
 #include "api/fs/fs.h"
+#include "cputopo.h"
 #include "smt.h"
 
-/**
+bool smt_on(const struct cpu_topology *topology)
- * hweight_str - Returns the number of bits set in str. Stops at first non-hex
- *	       or ',' character.
- */
-static int hweight_str(char *str)
-{
-	int result = 0;
-
-	while (*str) {
-		switch (*str++) {
-		case '0':
-		case ',':
-			break;
-		case '1':
-		case '2':
-		case '4':
-		case '8':
-			result++;
-			break;
-		case '3':
-		case '5':
-		case '6':
-		case '9':
-		case 'a':
-		case 'A':
-		case 'c':
-		case 'C':
-			result += 2;
-			break;
-		case '7':
-		case 'b':
-		case 'B':
-		case 'd':
-		case 'D':
-		case 'e':
-		case 'E':
-			result += 3;
-			break;
-		case 'f':
-		case 'F':
-			result += 4;
-			break;
-		default:
-			goto done;
-		}
-	}
-done:
-	return result;
-}
-
-int smt_on(void)
 {
 	static bool cached;
-	static int cached_result;
+	static bool cached_result;
-	int cpu;
+	int fs_value;
-	int ncpu;
 
 	if (cached)
 		return cached_result;
 
-	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {
+	if (sysfs__read_int("devices/system/cpu/smt/active", &fs_value) >= 0)
-		cached = true;
+		cached_result = (fs_value == 1);
-		return cached_result;
+	else
-	}
+		cached_result = cpu_topology__smt_on(topology);
 
-	cached_result = 0;
-	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/thread_siblings", cpu);
-		if (sysfs__read_str(fn, &str, &strlen) < 0) {
-			snprintf(fn, sizeof fn,
-				"devices/system/cpu/cpu%d/topology/core_cpus", cpu);
-			if (sysfs__read_str(fn, &str, &strlen) < 0)
-				continue;
-		}
-		/* Entry is hex, but does not have 0x, so need custom parser */
-		siblings = hweight_str(str);
-		free(str);
-		if (siblings > 1) {
-			cached_result = 1;
-			break;
-		}
-	}
 	cached = true;
 	return cached_result;
 }

tools/perf/util/smt.h

@@ -2,6 +2,9 @@
 #ifndef __SMT_H
 #define __SMT_H 1
 
-int smt_on(void);
+struct cpu_topology;
+
+/* Returns true if SMT (aka hyperthreading) is enabled. */
+bool smt_on(const struct cpu_topology *topology);
 
 #endif /* __SMT_H */