linux-kernel - Re: [patch] block: make struct block_device cacheline

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Message-ID: <5059E581.8030600@rsk.demon.co.uk>
Date:	Wed, 19 Sep 2012 16:32:17 +0100
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	jaxboe@...ionio.com, Mikulas Patocka <mpatocka@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] block: make struct block_device cacheline_aligned

On 19/09/12 15:59, Jeff Moyer wrote:
> Jeff Moyer <jmoyer@...hat.com> writes:
> 
>> Hi,
>>
>> When testing against a pcie ssd or a ramdisk, making the block device
>> structure cacheline_aligned provided a significant increase in
>> performance:
> 
> Self-NACK on this one.  This results in a ton of warnings:
> 
> include/linux/fs.h:727: warning: ???__section__??? attribute does not
> apply to types
> In file included from include/linux/debugfs.h:18,
>                  from kernel/trace/trace_probe.h:28,
>                  from kernel/trace/trace_kprobe.c:23:
> include/linux/fs.h:727: warning: ???__section__??? attribute does not
> apply to types
> 
> And that leaves me with the task of figuring out if/why this actually
> helps.
> 
> Cheers,
> Jeff
>>
Hi,
block_device sits in bdev_inode which is already cache line aligned as
they're allocated in a kmem_cache with HWALIGN set.
So I wonder if swapping the order of bdev & inode in bdev_inode will help?

So it becomes this :-
struct bdev_inode {
	struct inode vfs_inode;
	struct block_device bdev;
};


regards
Richard

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