linux-kernel - [PATCH] block: remove 16 bytes of padding from struct request on 64bits

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Message-ID: <1268907592.2047.6.camel@localhost>
Date:	Thu, 18 Mar 2010 10:19:52 +0000
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH]  block: remove 16 bytes of padding from struct request on
 64bits

Remove alignment padding to shrink struct request from 336 to 320 bytes
so needing one fewer cacheline and therefore removing 48 bytes from
struct request_queue.


Signed-off-by: Richard Kennedy <richard@....demon.co.uk>
---
patch against 2.6.34-rc1
compiled & tested on x86_64

regards
Richard


diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ebd22db..6b66438 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -158,7 +158,6 @@ enum rq_flag_bits {
 struct request {
 	struct list_head queuelist;
 	struct call_single_data csd;
-	int cpu;
 
 	struct request_queue *q;
 
@@ -166,9 +165,11 @@ struct request {
 	enum rq_cmd_type_bits cmd_type;
 	unsigned long atomic_flags;
 
+	int cpu;
+
 	/* the following two fields are internal, NEVER access directly */
-	sector_t __sector;		/* sector cursor */
 	unsigned int __data_len;	/* total data len */
+	sector_t __sector;		/* sector cursor */
 
 	struct bio *bio;
 	struct bio *biotail;
@@ -201,20 +202,20 @@ struct request {
 
 	unsigned short ioprio;
 
+	int ref_count;
+
 	void *special;		/* opaque pointer available for LLD use */
 	char *buffer;		/* kaddr of the current segment if available */
 
 	int tag;
 	int errors;
 
-	int ref_count;
-
 	/*
 	 * when request is used as a packet command carrier
 	 */
-	unsigned short cmd_len;
 	unsigned char __cmd[BLK_MAX_CDB];
 	unsigned char *cmd;
+	unsigned short cmd_len;
 
 	unsigned int extra_len;	/* length of alignment and padding */
 	unsigned int sense_len;


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