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

[Kevin Wolf]

Am 27.02.2013 um 16:38 hat Dietmar Maurer geschrieben:
> > > 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.)
> 
> Already tried that, but the 1000ns delay behaves better (again, just a 
> feeling, because
> I found no way to measure that behaviour).

Maybe mix the approaches? If there is no guest I/O going on, run the
backup at full speed, but if there is, then rate-limit it?

Kevin