Date:   Thu, 16 Feb 2023 20:24:42 +0000
Mime-Version: 1.0
Message-ID: <20230216202442.698394-1-jstultz@google.com>
Subject: [RESEND x2][PATCH v3] trace: Add trace points for tasklet entry/exit
From:   John Stultz <jstultz@google.com>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Lingutla Chandrasekhar <clingutla@codeaurora.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@kernel.org>, kernel-team@android.com,
        "J . Avila" <elavila@google.com>, John Stultz <jstultz@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

From: Lingutla Chandrasekhar <clingutla@codeaurora.org>

Tasklets are supposed to finish their work quickly and
should not block the current running process, but it is not
guaranteed that. Currently softirq_entry/exit can be used to
know total tasklets execution time, but not helpful to track
individual tasklet's execution time. With that we can't find
any culprit tasklet function, which is taking more time.

Add tasklet_entry/exit trace point support to track
individual tasklet execution.

Trivial usage example:
   # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_entry/enable
   # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_exit/enable
   # cat /sys/kernel/debug/tracing/trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 4/4   #P:4
 #
 #                                _-----=> irqs-off/BH-disabled
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              ||| / _-=> migrate-disable
 #                              |||| /     delay
 #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
 #              | |         |   |||||     |         |
           <idle>-0       [003] ..s1.   314.011428: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.011432: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.017369: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.017371: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func

This patch has been carried in the Android tree for awhile
so I wanted to submit it for review upstream. Feedback would
be appreciated!

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: kernel-team@android.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
[elavila: Port to android-mainline]
Signed-off-by: J. Avila <elavila@google.com>
[jstultz: Rebased to upstream, cut unused trace points, added
 comments for the tracepoints, reworded commit]
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Added tasklet pointer to the trace event as suggested by Steven
v3:
* Minor tweak to commit to show usage and output example
---
 include/trace/events/irq.h | 47 ++++++++++++++++++++++++++++++++++++++
 kernel/softirq.c           |  9 ++++++--
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h
index eeceafaaea4c..a07b4607b663 100644
--- a/include/trace/events/irq.h
+++ b/include/trace/events/irq.h
@@ -160,6 +160,53 @@ DEFINE_EVENT(softirq, softirq_raise,
 	TP_ARGS(vec_nr)
 );
 
+DECLARE_EVENT_CLASS(tasklet,
+
+	TP_PROTO(struct tasklet_struct *t, void *func),
+
+	TP_ARGS(t, func),
+
+	TP_STRUCT__entry(
+		__field(	void *,	tasklet)
+		__field(	void *,	func)
+	),
+
+	TP_fast_assign(
+		__entry->tasklet = t;
+		__entry->func = func;
+	),
+
+	TP_printk("tasklet=%ps function=%ps", __entry->tasklet, __entry->func)
+);
+
+/**
+ * tasklet_entry - called immediately before the tasklet is run
+ * @t: tasklet pointer
+ * @func: tasklet callback or function being run
+ *
+ * Used to find individual tasklet execution time
+ */
+DEFINE_EVENT(tasklet, tasklet_entry,
+
+	TP_PROTO(struct tasklet_struct *t, void *func),
+
+	TP_ARGS(t, func)
+);
+
+/**
+ * tasklet_exit - called immediately after the tasklet is run
+ * @t: tasklet pointer
+ * @func: tasklet callback or function being run
+ *
+ * Used to find individual tasklet execution time
+ */
+DEFINE_EVENT(tasklet, tasklet_exit,
+
+	TP_PROTO(struct tasklet_struct *t, void *func),
+
+	TP_ARGS(t, func)
+);
+
 #endif /*  _TRACE_IRQ_H */
 
 /* This part must be outside protection */
diff --git a/kernel/softirq.c b/kernel/softirq.c
index c8a6913c067d..1b725510dd0f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -793,10 +793,15 @@ static void tasklet_action_common(struct softirq_action *a,
 		if (tasklet_trylock(t)) {
 			if (!atomic_read(&t->count)) {
 				if (tasklet_clear_sched(t)) {
-					if (t->use_callback)
+					if (t->use_callback) {
+						trace_tasklet_entry(t, t->callback);
 						t->callback(t);
-					else
+						trace_tasklet_exit(t, t->callback);
+					} else {
+						trace_tasklet_entry(t, t->func);
 						t->func(t->data);
+						trace_tasklet_exit(t, t->func);
+					}
 				}
 				tasklet_unlock(t);
 				continue;
-- 
2.39.2.637.g21b0678d19-goog