[PATCH v1 5/8] perf topology: Add core_wide

Ian Rogers
2022-08-30T16:50:02Z

It is possible to optimize metrics when all SMT threads (CPUs) on a
core are measuring events in system wide mode. For example, TMA
metrics defines CORE_CLKS for Sandybrdige as:

if SMT is disabled:
CPU_CLK_UNHALTED.THREAD
if SMT is enabled and recording on all SMT threads:
CPU_CLK_UNHALTED.THREAD_ANY / 2
if SMT is enabled and not recording on all SMT threads:
(CPU_CLK_UNHALTED.THREAD/2)*
(1+CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE/CPU_CLK_UNHALTED.REF_XCLK )

That is two more events are necessary when not gathering counts on all
SMT threads. To distinguish all SMT threads on a core vs system wide
(all CPUs) call the new property core wide. Add a core wide test that
determines the property from user requested CPUs, the topology and
system wide. System wide is required as other processes running on a
SMT thread will change the counts.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/cputopo.c | 46 +++++++++++++++++++++++++++++++++++++++
tools/perf/util/cputopo.h | 3 +++
tools/perf/util/smt.c | 14 ++++++++++++
tools/perf/util/smt.h | 7 ++++++
4 files changed, 70 insertions(+)

diff --git a/tools/perf/util/cputopo.c b/tools/perf/util/cputopo.c
index 511002e52714..1a3ff6449158 100644
--- a/tools/perf/util/cputopo.c
+++ b/tools/perf/util/cputopo.c
@@ -172,6 +172,52 @@ bool cpu_topology__smt_on(const struct cpu_topology *topology)
return false;
}

+bool cpu_topology__core_wide(const struct cpu_topology *topology,
+ const char *user_requested_cpu_list)
+{
+ struct perf_cpu_map *user_requested_cpus;
+
+ /*
+ * If user_requested_cpu_list is empty then all CPUs are recorded and so
+ * core_wide is true.
+ */
+ if (!user_requested_cpu_list)
+ return true;
+
+ user_requested_cpus = perf_cpu_map__new(user_requested_cpu_list);
+ /* Check that every user requested CPU is the complete set of SMT threads on a core. */
+ for (u32 i = 0; i < topology->core_cpus_lists; i++) {
+ const char *core_cpu_list = topology->core_cpus_list[i];
+ struct perf_cpu_map *core_cpus = perf_cpu_map__new(core_cpu_list);
+ struct perf_cpu cpu;
+ int idx;
+ bool has_first, first = true;
+
+ perf_cpu_map__for_each_cpu(cpu, idx, core_cpus) {
+ if (first) {
+ has_first = perf_cpu_map__has(user_requested_cpus, cpu);
+ first = false;
+ } else {
+ /*
+ * If the first core CPU is user requested then
+ * all subsequent CPUs in the core must be user
+ * requested too. If the first CPU isn't user
+ * requested then none of the others must be
+ * too.
+ */
+ if (perf_cpu_map__has(user_requested_cpus, cpu) != has_first) {
+ perf_cpu_map__put(core_cpus);
+ perf_cpu_map__put(user_requested_cpus);
+ return false;
+ }
+ }
+ }
+ perf_cpu_map__put(core_cpus);
+ }
+ perf_cpu_map__put(user_requested_cpus);
+ return true;
+}
+
static bool has_die_topology(void)
{
char filename[MAXPATHLEN];
diff --git a/tools/perf/util/cputopo.h b/tools/perf/util/cputopo.h
index 469db775a13c..969e5920a00e 100644
--- a/tools/perf/util/cputopo.h
+++ b/tools/perf/util/cputopo.h
@@ -60,6 +60,9 @@ 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);
+/* Are the sets of SMT siblings all enabled or all disabled in user_requested_cpus. */
+bool cpu_topology__core_wide(const struct cpu_topology *topology,
+ const char *user_requested_cpu_list);

struct numa_topology *numa_topology__new(void);
void numa_topology__delete(struct numa_topology *tp);
diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index ce90c4ee4138..994e9e418227 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -21,3 +21,17 @@ bool smt_on(const struct cpu_topology *topology)
cached = true;
return cached_result;
}
+
+bool core_wide(bool system_wide, const char *user_requested_cpu_list,
+ const struct cpu_topology *topology)
+{
+ /* If not everything running on a core is being recorded then we can't use core_wide. */
+ if (!system_wide)
+ return false;
+
+ /* Cheap case that SMT is disabled and therefore we're inherently core_wide. */
+ if (!smt_on(topology))
+ return true;
+
+ return cpu_topology__core_wide(topology, user_requested_cpu_list);
+}
diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
index e26999c6b8d4..ae9095f2c38c 100644
--- a/tools/perf/util/smt.h
+++ b/tools/perf/util/smt.h
@@ -7,4 +7,11 @@ struct cpu_topology;
/* Returns true if SMT (aka hyperthreading) is enabled. */
bool smt_on(const struct cpu_topology *topology);

+/*
+ * Returns true when system wide and all SMT threads for a core are in the
+ * user_requested_cpus map.
+ */
+bool core_wide(bool system_wide, const char *user_requested_cpu_list,
+ const struct cpu_topology *topology);
+
#endif /* __SMT_H */
--
2.37.2.672.g94769d06f0-goog