Re: [Qemu-devel] [PATCH v4 00/10] main-loop: switch to g_poll(3) on POSIX hosts

[Paolo Bonzini]

Il 21/02/2013 17:29, Jan Kiszka ha scritto:
> In this context, I'd like to recall a detail: Real-time prioritization
> of those I/O threads will most probably require locking with
> prio-inversion avoidance (*). In that case external libs without a
> chance to tune or replace their internal locking (like glib) will be a
> no-go for those kind of I/O threads.
> 
> The glib mainloop might be fine for all the rest, but we will likely
> also need event loops with RT-compatible locking. So this refactoring
> should keep the door open for alternative implementations.

Yes, this refactoring is fine.  It doesn't use the glib mainloop any
more than before.  AioContext is fine as an RT-compatible event loop.
You can use both as a GSource or manually from a separate thread.

What would be more problematic is the chardev flow control patches,
which use the glib main loop directly.  I don't recall your KVM forum
presentation---did you need RT prioritization of the serial port too?

Paolo

> Jan
> 
> (*) Scenario: RT-iothread with highest prio wants to take a lock that is
> held briefly by low-prio maintenance thread which is interrupted by
> long-running medium-prio VCPU thread. This can delay or prevent the
> event injection. Of course, this depends on the existence of such
> dependencies.