linux-kernel - [PATCH v2] sched_ext: Add trace point to track sched

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Message-ID: <20250228085944.19451-1-changwoo@igalia.com>
Date: Fri, 28 Feb 2025 17:59:44 +0900
From: Changwoo Min <changwoo@...lia.com>
To: tj@...nel.org,
	void@...ifault.com,
	arighi@...dia.com
Cc: kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org,
	Changwoo Min <changwoo@...lia.com>
Subject: [PATCH v2] sched_ext: Add trace point to track sched_ext core events

Add tracing support to track sched_ext core events
(/sched_ext/sched_ext_event). This may be useful for debugging sched_ext
schedulers that trigger a particular event.

The trace point can be used as other trace points, so it can be used in,
for example, `perf trace` and BPF programs, as follows:

======
$> sudo perf trace -e sched_ext:sched_ext_event --filter 'name == "SCX_EV_ENQ_SLICE_DFL"'
======

======
struct tp_sched_ext_event {
	struct trace_entry ent;
	u32 __data_loc_name;
	u64 delta;
};

SEC("tracepoint/sched_ext/sched_ext_event")
int rtp_add_event(struct tp_sched_ext_event *ctx)
{
	char event_name[128];
	unsigned short offset = ctx->__data_loc_name & 0xFFFF;
        bpf_probe_read_str((void *)event_name, 128, (char *)ctx + offset);

	bpf_printk("name %s   delta %llu", event_name, ctx->delta);
	return 0;
}
======

Signed-off-by: Changwoo Min <changwoo@...lia.com>
---

ChangeLog v1 -> v2:
 - Rename @added field to @delta for clarity.
 - Rename sched_ext_add_event to sched_ext_event.
 - Drop the @offset field to avoid the potential misuse of non-portable numbers.

 include/trace/events/sched_ext.h | 19 +++++++++++++++++++
 kernel/sched/ext.c               |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/include/trace/events/sched_ext.h b/include/trace/events/sched_ext.h
index fe19da7315a9..b73499981682 100644
--- a/include/trace/events/sched_ext.h
+++ b/include/trace/events/sched_ext.h
@@ -26,6 +26,25 @@ TRACE_EVENT(sched_ext_dump,
 	)
 );
 
+TRACE_EVENT(sched_ext_event,
+	    TP_PROTO(const char *name, __u64 delta),
+	    TP_ARGS(name, delta),
+
+	TP_STRUCT__entry(
+		__string(name, name)
+		__field(	__u64,		delta		)
+	),
+
+	TP_fast_assign(
+		__assign_str(name);
+		__entry->delta		= delta;
+	),
+
+	TP_printk("name %s delta %llu",
+		  __get_str(name), __entry->delta
+	)
+);
+
 #endif /* _TRACE_SCHED_EXT_H */
 
 /* This part must be outside protection */
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 986b655911df..53729c584b63 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1554,6 +1554,7 @@ static DEFINE_PER_CPU(struct scx_event_stats, event_stats_cpu);
  */
 #define scx_add_event(name, cnt) do {						\
 	this_cpu_add(event_stats_cpu.name, cnt);				\
+	trace_sched_ext_event(#name, cnt);					\
 } while(0)
 
 /**
@@ -1565,6 +1566,7 @@ static DEFINE_PER_CPU(struct scx_event_stats, event_stats_cpu);
  */
 #define __scx_add_event(name, cnt) do {						\
 	__this_cpu_add(event_stats_cpu.name, cnt);				\
+	trace_sched_ext_event(#name, cnt);					\
 } while(0)
 
 /**
-- 
2.48.1