linux-kernel - [PATCH 12/16] tty: Avoid false-sharing flip buffer ptrs

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Message-Id: <1366039567-8620-13-git-send-email-peter@hurleysoftware.com>
Date:	Mon, 15 Apr 2013 11:26:03 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 12/16] tty: Avoid false-sharing flip buffer ptrs

Separate the head and tail ptrs to avoid cache-line contention
(so called 'false-sharing') between concurrent threads.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 include/linux/tty.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 094a909..08633e0 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -65,13 +65,13 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
 
 
 struct tty_bufhead {
+	struct tty_buffer *head;	/* Queue head */
 	struct work_struct work;
 	struct mutex flush_mutex;
 	struct tty_buffer sentinel;
-	struct tty_buffer *head;	/* Queue head */
-	struct tty_buffer *tail;	/* Active buffer */
 	struct llist_head free;		/* Free queue head */
 	atomic_t	   memory_used; /* In-use buffers excluding free list */
+	struct tty_buffer *tail;	/* Active buffer */
 };
 /*
  * When a break, frame error, or parity error happens, these codes are
-- 
1.8.1.2

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