linux-kernel - [PATCH 02/58] serial: Move sysrq members above

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Message-Id: <20191213000657.931618-3-dima@arista.com>
Date:   Fri, 13 Dec 2019 00:06:01 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Vasiliy Khoruzhick <vasilykh@...sta.com>,
        linux-serial@...r.kernel.org
Subject: [PATCH 02/58] serial: Move sysrq members above

At the current place members those follow are:
:	upf_t			flags;
:	upstat_t		status;
:	int			hw_stopped;
:	unsigned int		mctrl;
:	unsigned int		timeout;
:	unsigned int		type;
:	const struct uart_ops	*ops;

Together, they give (*ops) 8-byte align on 64-bit platforms.
And `sysrq_ch` introduces 4-byte padding.

On the other side, above:
:	struct device		*dev;
:	unsigned char		hub6;
:	unsigned char		suspended;
:	unsigned char		unused[2];
:	const char		*name;

Adds another 4-byte padding.

Moving sysrq members just before `hub6` allows to save 8 bytes
per-uart_port on 64-bit platforms:
On my gcc, x86_64 sizeof(struct uart_port) goes from 528 to 520.

Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 include/linux/serial_core.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 2b78cc734719..bbbe57bf5163 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -161,11 +161,6 @@ struct uart_port {
 	struct uart_icount	icount;			/* statistics */
 
 	struct console		*cons;			/* struct console, if any */
-#if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(SUPPORT_SYSRQ)
-	unsigned long		sysrq;			/* sysrq timeout */
-	unsigned int		sysrq_ch;		/* char for sysrq */
-#endif
-
 	/* flags must be updated while holding port mutex */
 	upf_t			flags;
 
@@ -244,6 +239,12 @@ struct uart_port {
 	resource_size_t		mapbase;		/* for ioremap */
 	resource_size_t		mapsize;
 	struct device		*dev;			/* parent device */
+
+#if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(SUPPORT_SYSRQ)
+	unsigned long		sysrq;			/* sysrq timeout */
+	unsigned int		sysrq_ch;		/* char for sysrq */
+#endif
+
 	unsigned char		hub6;			/* this should be in the 8250 driver */
 	unsigned char		suspended;
 	unsigned char		unused[2];
-- 
2.24.0