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

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Date:	Mon, 15 Feb 2010 09:16:26 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Richard Kennedy <richard@....demon.co.uk>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Corrado Zoccolo <czoccolo@...il.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cfq: reorder cfq_queue removing padding on 64bit &
	allowing more objects/slab in it's kmem_cache

On Mon, Feb 15, 2010 at 02:10:36PM +0000, Richard Kennedy wrote:
> 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
> 
> regards
> Richard
> 
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 023f4e6..db4c127 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -116,10 +116,10 @@ struct cfq_queue {
>  	unsigned long dispatch_start;
>  	unsigned int allocated_slice;
>  	/* time when first request from queue completed and slice started. */
> +	unsigned int slice_dispatch;

Can you move it above the comment. The comment describes "slice_start" and
now comment and variable have been separated.

Vivek

>  	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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