linux-kernel - Re: [REVIEW] NVM Express driver

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Message-ID: <20110304144633.GB3663@linux.intel.com>
Date:	Fri, 4 Mar 2011 09:46:33 -0500
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [REVIEW] NVM Express driver

On Fri, Mar 04, 2011 at 08:06:45AM -0500, Christoph Hellwig wrote:
> What's the reason to make this a make_request based driver?  That loses
> all the intelligence that has been put into the queueing layer, like I/O
> bandwith controlling and fair scheduling.  Is it just queue_lock
> contention?  If so it would be great if you could help with testing
> Jens' stack-plug and request allocation scalability patches.

The hardware has the ability to do I/O bandwidth control and fair
scheduling (albeit on a fairly coarse granularity).  By doing it in
software, all we're doing for these devices is increasing I/O latency
and burning CPU cycles.
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