linux-kernel - Re: [PATCH 10/11] VFS: Cache request_queue in struct block

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Message-ID: <20110819141409.GD18656@redhat.com>
Date:	Fri, 19 Aug 2011 10:14:09 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [PATCH 10/11] VFS: Cache request_queue in struct block_device

On Thu, Aug 18, 2011 at 02:03:56PM -0700, Andi Kleen wrote:
> 
> >Is the performance gain because of this one less dereference really
> >substantial.
> Yes it is measurable on a large macro benchmark.
> 
> The gain is from doing the prefetch early enough, and that needs the
> additional pointer.

So it gives you extra .3% (as mentioned in your first mail). IMHO, for
.3% we should not cache extra request queue pointer.

Thanks
Vivek
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