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From:   sunliming <sunliming@kylinos.cn>
To:     rostedt@goodmis.org, mingo@kernel.org
Cc:     linux-kernel@vger.kernel.org, kelulanainsley@gmail.com,
        sunliming <sunliming@kylinos.cn>
Subject: [PATCH 2/5] ring-buffer: Remove absolute timestamp from add_timestamp logic
Date:   Tue, 18 Oct 2022 20:00:53 +0800
Message-Id: <20221018120056.1321426-3-sunliming@kylinos.cn>
In-Reply-To: <20221018120056.1321426-1-sunliming@kylinos.cn>
References: <20221018120056.1321426-1-sunliming@kylinos.cn>
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Remove absolute timestamp from add_timestamp logic.

Signed-off-by: sunliming <sunliming@kylinos.cn>
---
 kernel/trace/ring_buffer.c | 49 +++++++++++++-------------------------
 1 file changed, 17 insertions(+), 32 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 199759c73519..ab0aef15f82a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -436,14 +436,12 @@ struct rb_event_info {
  * Used for the add_timestamp
  *  NONE
  *  EXTEND - wants a time extend
- *  ABSOLUTE - the buffer requests all events to have absolute time stamps
  *  FORCE - force a full time stamp.
  */
 enum {
 	RB_ADD_STAMP_NONE		= 0,
 	RB_ADD_STAMP_EXTEND		= BIT(1),
-	RB_ADD_STAMP_ABSOLUTE		= BIT(2),
-	RB_ADD_STAMP_FORCE		= BIT(3)
+	RB_ADD_STAMP_FORCE		= BIT(2)
 };
 /*
  * Used for which event context the event is in.
@@ -2832,8 +2830,7 @@ static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 				      u64 *delta,
 				      unsigned int *length)
 {
-	bool abs = info->add_timestamp &
-		(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
+	bool abs = info->add_timestamp & RB_ADD_STAMP_FORCE;
 
 	if (unlikely(info->delta > (1ULL << 59))) {
 		/*
@@ -3435,8 +3432,7 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
 	if (tail == CHECK_FULL_PAGE) {
 		full = true;
 		tail = local_read(&bpage->commit);
-	} else if (info->add_timestamp &
-		   (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
+	} else if (info->add_timestamp & RB_ADD_STAMP_FORCE) {
 		/* Ignore events with absolute time stamps */
 		return;
 	}
@@ -3535,23 +3531,19 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	barrier();
 	info->ts = rb_time_stamp(cpu_buffer->buffer);
 
-	if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
-		info->delta = info->ts;
+	/*
+	 * If interrupting an event time update, we may need an
+	 * absolute timestamp.
+	 * Don't bother if this is the start of a new page (w == 0).
+	 */
+	if (unlikely(!a_ok || !b_ok || (info->before != info->after && w))) {
+		info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
+		info->length += RB_LEN_TIME_EXTEND;
 	} else {
-		/*
-		 * If interrupting an event time update, we may need an
-		 * absolute timestamp.
-		 * Don't bother if this is the start of a new page (w == 0).
-		 */
-		if (unlikely(!a_ok || !b_ok || (info->before != info->after && w))) {
-			info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
+		info->delta = info->ts - info->after;
+		if (unlikely(test_time_stamp(info->delta))) {
+			info->add_timestamp |= RB_ADD_STAMP_EXTEND;
 			info->length += RB_LEN_TIME_EXTEND;
-		} else {
-			info->delta = info->ts - info->after;
-			if (unlikely(test_time_stamp(info->delta))) {
-				info->add_timestamp |= RB_ADD_STAMP_EXTEND;
-				info->length += RB_LEN_TIME_EXTEND;
-			}
 		}
 	}
 
@@ -3586,8 +3578,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		barrier();
  /*E*/		s_ok = rb_time_read(&cpu_buffer->before_stamp, &save_before);
 		RB_WARN_ON(cpu_buffer, !s_ok);
-		if (likely(!(info->add_timestamp &
-			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
+		if (likely(!(info->add_timestamp & RB_ADD_STAMP_FORCE)))
 			/* This did not interrupt any time update */
 			info->delta = info->ts - info->after;
 		else
@@ -3644,8 +3635,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	 * If this is the first commit on the page, then it has the same
 	 * timestamp as the page itself.
 	 */
-	if (unlikely(!tail && !(info->add_timestamp &
-				(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
+	if (unlikely(!tail && !(info->add_timestamp & RB_ADD_STAMP_FORCE)))
 		info->delta = 0;
 
 	/* We reserved something on the buffer */
@@ -3698,12 +3688,7 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 
 	info.length = rb_calculate_event_length(length);
 
-	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
-		add_ts_default = RB_ADD_STAMP_ABSOLUTE;
-		info.length += RB_LEN_TIME_EXTEND;
-	} else {
-		add_ts_default = RB_ADD_STAMP_NONE;
-	}
+	add_ts_default = RB_ADD_STAMP_NONE;
 
  again:
 	info.add_timestamp = add_ts_default;
-- 
2.25.1