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

[Andi Kleen <andi@xxxxxxxxxxxxxx>]

Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> writes:
> > Therefore, I think that it is better to develop OS-agnostic I/O control.
> 
> 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.

And if CFQ2 can manage hundreds of processes I don't see why it
couldn't manage hundreds of guests. Although you probably should not
put that many on a single device anyways; or rather if it's a single
device for that many it's likely a RAM backed big storage box that
doesn't need much scheduling anyways. 

The claim that CFQ2 is desktop oriented in this thread earlier is also
not true. The desktop oriented scheduler is more AS and CFQ2 is widely
and successfully used in server applications.

-Andi


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