Re: [Qemu-devel] [PATCH v4 2/6] add basic backup support to block driver

[Stefan Hajnoczi]

On Tue, Feb 26, 2013 at 05:02:19PM +0000, Dietmar Maurer wrote:
> > If you want to implement an alternative to rate-limiting, please do it in a
> > separate patch series and make it work for all block job types.
> 
> Well, I hoped you can see how to fix that. I guess the same applies for other 
> types of block
> jobs, and I simply found no other solution.
> 
> Adding and IO queue and implement a scheduler is likely not what we want to 
> do. 

The starting point for something smarter than just no policy or
rate-limiting is BlockDriverState->tracked_requests.  block.c keeps
track of active requests using this list.

The simplest policy using bs->tracked_requests is to only submit block
job I/O requests when the list is empty.

Want to try this approach?  (The drawback is that the guest can starve
the block job by submitting I/O all the time.)

Stefan