linux-kernel - Re: [patch] speed up single bio

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Date:	Mon, 4 Dec 2006 21:43:51 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] speed up single bio_vec allocation

On Mon, Dec 04 2006, Chen, Kenneth W wrote:
> > [...]
> > 
> > Another idea would be to kill SLAB_HWCACHE_ALIGN (it's pretty pointless,
> > I bet), and always alloc sizeof(*bio) + sizeof(*bvl) in one go when a
> > bio is allocated. It doesn't add a lot of overhead even for the case
> > where we do > 1 page bios, and it gets rid of the dual allocation for
> > the 1 page bio.
> 
> I will try that too.  I'm a bit touchy about sharing a cache line for
> different bio.  But given that there are 200,000 I/O per second we are
> currently pushing the kernel, the chances of two cpu working on two
> bio that sits in the same cache line are pretty small.

Yep I really think so. Besides, it's not like we are repeatedly writing
to these objects in the first place.

-- 
Jens Axboe

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