[PATCH v1 4/8] perf smt: Compute SMT from topology

Ian Rogers
2022-08-30T16:49:51Z

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>
---
tools/perf/tests/expr.c | 24 ++++++----
tools/perf/util/cputopo.c | 15 +++++++
tools/perf/util/cputopo.h | 2 +
tools/perf/util/expr.c | 9 ++--
tools/perf/util/smt.c | 95 ++++-----------------------------------
tools/perf/util/smt.h | 5 ++-
6 files changed, 49 insertions(+), 101 deletions(-)

diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index 7ca5e37de560..db736ed49556 100644
--- a/tools/perf/tests/expr.c
+++ b/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",
- 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,
- smt_on() ? "EVENT1" : "EVENT2",
- (void **)&val_ptr));
-
+ {
+ struct cpu_topology *topology = cpu_topology__new();
+ bool smton = smt_on(topology);
+
+ 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",
diff --git a/tools/perf/util/cputopo.c b/tools/perf/util/cputopo.c
index d275d843c155..511002e52714 100644
--- a/tools/perf/util/cputopo.c
+++ b/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];
diff --git a/tools/perf/util/cputopo.h b/tools/perf/util/cputopo.h
index 854e18f9041e..469db775a13c 100644
--- a/tools/perf/util/cputopo.h
+++ b/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);
diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index 00bde682e743..8aa7dafa18b3 100644
--- a/tools/perf/util/expr.c
+++ b/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;
diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 8fed03283c85..ce90c4ee4138 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -1,100 +1,23 @@
// SPDX-License-Identifier: GPL-2.0-only
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
-#include <linux/bitops.h>
+#include <string.h>
#include "api/fs/fs.h"
+#include "cputopo.h"
#include "smt.h"

-/**
- * 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)
+bool smt_on(const struct cpu_topology *topology)
{
static bool cached;
- static int cached_result;
- int cpu;
- int ncpu;
+ static bool cached_result;
+ int fs_value;

if (cached)
return cached_result;

- if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {
- cached = true;
- return cached_result;
- }
-
- 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];
+ if (sysfs__read_int("devices/system/cpu/smt/active", &fs_value) >= 0)
+ cached_result = (fs_value == 1);
+ else
+ cached_result = cpu_topology__smt_on(topology);

- 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;
}
diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
index a98d65808f6a..e26999c6b8d4 100644
--- a/tools/perf/util/smt.h
+++ b/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 */
--
2.37.2.672.g94769d06f0-goog