linux-kernel - [PATCH v2 06/17] serial: max310x: remove holes in struct max310x

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Date: Thu, 18 Jan 2024 10:22:02 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	cosmin.tanislav@...log.com,
	andy.shevchenko@...il.com,
	shc_work@...l.ru
Cc: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	hugo@...ovil.com,
	Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: [PATCH v2 06/17] serial: max310x: remove holes in struct max310x_devtype

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

Running pahole shows that there are some holes within the
max310x_devtype structure.

Remove holes and optimize alignment by reorganizing structure members.

This can also lead to data structure size reduction for some CPUs.

On 64-bit CPU (arm64):
Before:
    /* size: 40, cachelines: 1, members: 6 */
    /* sum members: 34, holes: 2, sum holes: 6 */
    /* last cacheline: 40 bytes */
After:
    /* size: 40, cachelines: 1, members: 6 */
    /* padding: 6 */
    /* last cacheline: 40 bytes */

On 32-bit CPU (i386):
Before:
    /* size: 32, cachelines: 1, members: 6 */
    /* sum members: 26, holes: 2, sum holes: 6 */
    /* last cacheline: 32 bytes */
After:
    /* size: 24, cachelines: 1, members: 8 */
    /* padding: 2 */
    /* last cacheline: 24 bytes */

Suggested-by: Andy Shevchenko <andy.shevchenko@...il.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 drivers/tty/serial/max310x.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index 27c8ec956691..21f2fa3a91e5 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -258,11 +258,11 @@ struct max310x_devtype {
 		unsigned short min;
 		unsigned short max;
 	} slave_addr;
-	char	name[9];
 	int	nr;
-	u8	mode1;
 	int	(*detect)(struct device *);
 	void	(*power)(struct uart_port *, int);
+	char	name[9];
+	u8	mode1;
 };
 
 struct max310x_one {
-- 
2.39.2