linux-kernel - Re: [PATCH v2] cfq: reorder cfq_queue removing padding on 64bit & allowing more objects/slab in it's kmem

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Message-ID: <1266251188.7362.3.camel@localhost>
Date:	Mon, 15 Feb 2010 16:26:28 +0000
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <jens.axboe@...cle.com>
Cc:	Corrado Zoccolo <czoccolo@...il.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2]  cfq: reorder cfq_queue removing padding on 64bit &
 allowing more objects/slab in it's kmem_cache

This removes 8 bytes of padding from struct cfq_queue on 64 bit builds,
shrinking it's size to 256 bytes, so fitting into 1 fewer cachelines and
allowing 1 more object/slab in it's kmem_cache.
 

Signed-off-by: Richard Kennedy <richard@....demon.co.uk>
----
patch against 2.6.33-rc8
tested on x86_64 AMDX2


diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 023f4e6..e3dedfd 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -115,11 +115,11 @@ struct cfq_queue {
 	/* time when queue got scheduled in to dispatch first request. */
 	unsigned long dispatch_start;
 	unsigned int allocated_slice;
+	unsigned int slice_dispatch;
 	/* time when first request from queue completed and slice started. */
 	unsigned long slice_start;
 	unsigned long slice_end;
 	long slice_resid;
-	unsigned int slice_dispatch;
 
 	/* pending metadata requests */
 	int meta_pending;
@@ -130,13 +130,13 @@ struct cfq_queue {
 	unsigned short ioprio, org_ioprio;
 	unsigned short ioprio_class, org_ioprio_class;
 
+	pid_t pid;
+
 	unsigned int seek_samples;
 	u64 seek_total;
 	sector_t seek_mean;
 	sector_t last_request_pos;
 
-	pid_t pid;
-
 	struct cfq_rb_root *service_tree;
 	struct cfq_queue *new_cfqq;
 	struct cfq_group *cfqg;


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