[PATCH v6 1/9] perf report: Add machine parallelism

Dmitry Vyukov
2025-02-07T11:41:15Z

Add calculation of the current parallelism level (number of threads actively
running on CPUs). The parallelism level can be shown in reports on its own,
and to calculate latency overheads.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
tools/perf/builtin-report.c | 1 +
tools/perf/util/addr_location.c | 1 +
tools/perf/util/addr_location.h | 2 ++
tools/perf/util/event.c | 3 +++
tools/perf/util/machine.c | 7 +++++++
tools/perf/util/machine.h | 6 ++++++
6 files changed, 20 insertions(+)

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index f5fbd670d619a..0d9bd090eda71 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -1568,6 +1568,7 @@ int cmd_report(int argc, const char **argv)
report.tool.cgroup = perf_event__process_cgroup;
report.tool.exit = perf_event__process_exit;
report.tool.fork = perf_event__process_fork;
+ report.tool.context_switch = perf_event__process_switch;
report.tool.lost = perf_event__process_lost;
report.tool.read = process_read_event;
report.tool.attr = process_attr;
diff --git a/tools/perf/util/addr_location.c b/tools/perf/util/addr_location.c
index 51825ef8c0ab7..007a2f5df9a6a 100644
--- a/tools/perf/util/addr_location.c
+++ b/tools/perf/util/addr_location.c
@@ -17,6 +17,7 @@ void addr_location__init(struct addr_location *al)
al->cpumode = 0;
al->cpu = 0;
al->socket = 0;
+ al->parallelism = 1;
}

/*
diff --git a/tools/perf/util/addr_location.h b/tools/perf/util/addr_location.h
index d8ac0428dff23..36aaa45445f24 100644
--- a/tools/perf/util/addr_location.h
+++ b/tools/perf/util/addr_location.h
@@ -21,6 +21,8 @@ struct addr_location {
u8 cpumode;
s32 cpu;
s32 socket;
+ /* Same as machine.parallelism but within [1, nr_cpus]. */
+ int parallelism;
};

void addr_location__init(struct addr_location *al);
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index aac96d5d19170..2f10e31157572 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -767,6 +767,9 @@ int machine__resolve(struct machine *machine, struct addr_location *al,
al->socket = env->cpu[al->cpu].socket_id;
}

+ /* Account for possible out-of-order switch events. */
+ al->parallelism = max(1, min(machine->parallelism, machine__nr_cpus_avail(machine)));
+
if (al->map) {
if (symbol_conf.dso_list &&
(!dso || !(strlist__has_entry(symbol_conf.dso_list,
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 2d51badfbf2e2..0e65c5377f983 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -94,6 +94,8 @@ int machine__init(struct machine *machine, const char *root_dir, pid_t pid)
machine->comm_exec = false;
machine->kernel_start = 0;
machine->vmlinux_map = NULL;
+ /* There is no initial context switch in, so we start at 1. */
+ machine->parallelism = 1;

machine->root_dir = strdup(root_dir);
if (machine->root_dir == NULL)
@@ -677,8 +679,11 @@ int machine__process_aux_output_hw_id_event(struct machine *machine __maybe_unus
int machine__process_switch_event(struct machine *machine __maybe_unused,
union perf_event *event)
{
+ bool out = event->header.misc & PERF_RECORD_MISC_SWITCH_OUT;
+
if (dump_trace)
perf_event__fprintf_switch(event, stdout);
+ machine->parallelism += out ? -1 : 1;
return 0;
}

@@ -1900,6 +1905,8 @@ int machine__process_exit_event(struct machine *machine, union perf_event *event
if (dump_trace)
perf_event__fprintf_task(event, stdout);

+ /* There is no context switch out before exit, so we decrement here. */
+ machine->parallelism--;
if (thread != NULL) {
if (symbol_conf.keep_exited_threads)
thread__set_exited(thread, /*exited=*/true);
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 2e5a4cb342d82..a5f28652873ce 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -50,6 +50,12 @@ struct machine {
u64 text_start;
u64 text_end;
} sched, lock, traceiter, trace;
+ /*
+ * The current parallelism level (number of threads that run on CPUs).
+ * This value can be less than 1, or larger than the total number
+ * of CPUs, if events are poorly ordered.
+ */
+ int parallelism;
pid_t *current_tid;
size_t current_tid_sz;
union { /* Tool specific area */