Re: [Qemu-devel] [RFC v2 0/8] monitor: allow per-monitor thread

[Dr. David Alan Gilbert]

* Stefan Hajnoczi (address@hidden) wrote:
> On Wed, Aug 23, 2017 at 02:51:03PM +0800, Peter Xu wrote:
> > The root problem is that, monitor commands are all handled in main
> > loop thread now, no matter how many monitors we specify. And, if main
> > loop thread hangs due to some reason, all monitors will be stuck.
> 
> I see a larger issue with postcopy: existing QEMU code assumes that
> guest memory access is instantaneous.
> 
> Postcopy breaks this assumption and introduces blocking points that can
> now take unbounded time.
> 
> This problem isn't specific to the monitor.  It can also happen to other
> components in QEMU like the gdbstub.
> 
> Do we need an asynchronous memory API?  Synchronous memory access should
> only be allowed in vcpu threads.

It would probably be useful for gdbstub where the overhead of async
doesn't matter;  but doing that for all IO emulation is hard.

Dave

> Stefan
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK