linux-kernel - [PATCH 2/2] ring-buffer: Reuse rb_watermark

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Date: Tue, 12 Mar 2024 07:54:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 2/2] ring-buffer: Reuse rb_watermark_hit() for the poll logic

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

The check for knowing if the poll should wait or not is basically the
exact same logic as rb_watermark_hit(). The only difference is that
rb_watermark_hit() also handles the !full case. But for the full case, the
logic is the same. Just call that instead of duplicating the code in
ring_buffer_poll_wait().

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/ring_buffer.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index adfe603a769b..6ef763f57c66 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -963,21 +963,16 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
 
 		poll_wait(filp, &rbwork->full_waiters, poll_table);
 
-		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
-		if (!cpu_buffer->shortest_full ||
-		    cpu_buffer->shortest_full > full)
-			cpu_buffer->shortest_full = full;
-		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
-		if (full_hit(buffer, cpu, full))
+		if (rb_watermark_hit(buffer, cpu, full))
 			return EPOLLIN | EPOLLRDNORM;
 		/*
 		 * Only allow full_waiters_pending update to be seen after
-		 * the shortest_full is set. If the writer sees the
-		 * full_waiters_pending flag set, it will compare the
-		 * amount in the ring buffer to shortest_full. If the amount
-		 * in the ring buffer is greater than the shortest_full
-		 * percent, it will call the irq_work handler to wake up
-		 * this list. The irq_handler will reset shortest_full
+		 * the shortest_full is set (in rb_watermark_hit). If the
+		 * writer sees the full_waiters_pending flag set, it will
+		 * compare the amount in the ring buffer to shortest_full.
+		 * If the amount in the ring buffer is greater than the
+		 * shortest_full percent, it will call the irq_work handler
+		 * to wake up this list. The irq_handler will reset shortest_full
 		 * back to zero. That's done under the reader_lock, but
 		 * the below smp_mb() makes sure that the update to
 		 * full_waiters_pending doesn't leak up into the above.
-- 
2.43.0