From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <andi@firstfloor.org>
Subject: Re: Is QoS of virtual disk not necessary?
Date: Fri, 24 Aug 2007 22:53:50 +0200
Message-ID: <20070824205350.GA23558@one.firstfloor.org>
References: <p73d4xcyhbo.fsf@bingen.suse.de>
	<C2F4D6B6.148D3%Keir.Fraser@cl.cam.ac.uk>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <xen-devel-bounces@lists.xensource.com>
Content-Disposition: inline
In-Reply-To: <C2F4D6B6.148D3%Keir.Fraser@cl.cam.ac.uk>
List-Unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
Cc: Satoshi Uchida <s-uchida@ap.jp.nec.com>, Andi Kleen <andi@firstfloor.org>, xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

On Fri, Aug 24, 2007 at 06:40:54PM +0100, Keir Fraser wrote:
> On 24/8/07 18:26, "Andi Kleen" <andi@firstfloor.org> wrote:
> 
> >> Another nice thing would be that if we do not use CFQ then we do not need a
> >> kernel thread per VBD.
> > 
> > It would be probably easy to extend CFQ2 to use an user passed identifier
> > instead of per task for sharing if that's your goal. For a kernel driver
> > like blkback you could just switch around multiple current->io_contexts.
> 
> Does current->io_context get latched before submit_bh() (or whatever similar
> function it is we use) returns? Is this true even in older 2.6 kernels with
> old CFQ?

It obviously has to because you could exit in the next call.
The context is reference counted and lazily freed.

-Andi