linux-kernel - Re: [PATCH 1/3] block: add queue flag for paravirt frontend drivers

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Date:	Wed, 5 Nov 2008 10:20:17 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>, rusty@...tcorp.com.au,
	linux-kernel@...r.kernel.org, jeremy@...source.com
Subject: Re: [PATCH 1/3] block: add queue flag for paravirt frontend drivers

On Tue, Nov 04 2008, Jeremy Fitzhardinge wrote:
> Jens Axboe wrote:
> >On Mon, Oct 27 2008, Fernando Luis Vázquez Cao wrote:
> >
> >>As is the case with SSD devices, we do not want to idle in AS/CFQ when
> >>the block device is a paravirt front-end driver. This patch adds a flag
> >>(QUEUE_FLAG_VIRT) which should be used by front-end drivers such as
> >>virtio_blk and xen-blkfront to indicate a paravirtualized device.
> >>
> >
> >All three patches look fine, although we could just reuse
> >QUEUE_FLAG_NONROT directly. But I agree it makes sense to make the
> >distinction, so I've just applied 1-3.
> >
> 
> I guess in theory you could imagine that the virtual device is mapped
> directly onto a physical device, and the host OS does no scheduling, in
> which case it would be appropriate for the guest do the work.  But I
> think otherwise this makes sense.

For that specific case, it should just not set the flag.

-- 
Jens Axboe

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