perf sched: Sanity check context switch events
Use 'perf sched latency' to track the current task based on
context-switch events, and flag the cases where there's some
impossible transition: such as a PID being switched out that
was not switched in.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 1f0f9be..2d54236 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -119,6 +119,7 @@
static unsigned long nr_timestamps;
static unsigned long nr_unordered_timestamps;
static unsigned long nr_state_machine_bugs;
+static unsigned long nr_context_switch_bugs;
static unsigned long nr_events;
static unsigned long nr_lost_chunks;
static unsigned long nr_lost_events;
@@ -1399,6 +1400,14 @@
printf(" (due to lost events?)");
printf("\n");
}
+ if (nr_context_switch_bugs && nr_timestamps) {
+ printf(" INFO: %.3f%% context switch bugs (%ld out of %ld)",
+ (double)nr_context_switch_bugs/(double)nr_timestamps*100.0,
+ nr_context_switch_bugs, nr_timestamps);
+ if (nr_lost_events)
+ printf(" (due to lost events?)");
+ printf("\n");
+ }
printf("\n");
}
@@ -1425,10 +1434,16 @@
trace_handler->wakeup_event(&wakeup_event, event, cpu, timestamp, thread);
}
+/*
+ * Track the current task - that way we can know whether there's any
+ * weird events, such as a task being switched away that is not current.
+ */
+static u32 curr_pid[MAX_CPUS] = { [0 ... MAX_CPUS-1] = -1 };
+
static void
process_sched_switch_event(struct raw_event_sample *raw,
struct event *event,
- int cpu __used,
+ int cpu,
u64 timestamp __used,
struct thread *thread __used)
{
@@ -1444,6 +1459,16 @@
FILL_FIELD(switch_event, next_pid, event, raw->data);
FILL_FIELD(switch_event, next_prio, event, raw->data);
+ if (curr_pid[cpu] != (u32)-1) {
+ /*
+ * Are we trying to switch away a PID that is
+ * not current?
+ */
+ if (curr_pid[cpu] != switch_event.prev_pid)
+ nr_context_switch_bugs++;
+ }
+ curr_pid[cpu] = switch_event.next_pid;
+
trace_handler->switch_event(&switch_event, event, cpu, timestamp, thread);
}