[Xen-devel] Re: Is QoS of virtual disk not necessary?

[Andi Kleen <andi@xxxxxxxxxxxxxx>]

On Fri, Aug 24, 2007 at 06:40:54PM +0100, Keir Fraser wrote:
> On 24/8/07 18:26, "Andi Kleen" <andi@xxxxxxxxxxxxxx> 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

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