linux-kernel - [for-next][PATCH 14/18] ring-buffer: Mark the !tail (crossing a page) as unlikely

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Date:   Thu, 02 Jul 2020 17:58:26 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [for-next][PATCH 14/18] ring-buffer: Mark the !tail (crossing a page) as unlikely

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

It is the uncommon case where an event crosses a sub buffer boundary (page)
mark that check at the end of reserving an event as unlikely.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ed1941304f69..888bc9177937 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3260,7 +3260,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	 * If this is the first commit on the page, then update
 	 * its timestamp.
 	 */
-	if (!tail)
+	if (unlikely(!tail))
 		tail_page->page->time_stamp = info->ts;
 
 	/* account for these added bytes */
-- 
2.26.2