Re: [Qemu-devel] QEMU and Real Time OS

[Marc Marí]

El Fri, 30 Jan 2015 08:37:47 +0100
Jan Kiszka <address@hidden> escribió:
> On 2015-01-30 00:06, Paolo Bonzini wrote:
> > 
> > 
> > On 29/01/2015 20:37, Marc Marí wrote:
> >> Is this an expected behaviour? I can't see why.
> >>
> >> I'd like to know if there is a certain reason why it doesn't work.
> >> Or if it should work and the problem is too much I/O overhead. Or
> >> any other hint to understand it.
> > 
> > It is due to latencies in the host.  You need at least to use
> > preempt-rt kernels in the host as well.
> 
> That alone won't help much. You also need to fine-tune the guest to
> avoid running into QEMU locks that continuously synchronizes the guest
> on things like VGA or disk I/O emulation.
> 
> When using KVM, thus being able to run VCPUs widely independent of
> each other and the device models, you need to push cyclictest on an
> isolated second virtual CPU of the guest. Luiz and Marcelo can
> probably confirm this based on their ongoing experiments.
> 
> With TCG, we would first of all have to make it true SMP and
> independent of the I/O device lock. That's what Frederic is working
> on [1].
> 
> Jan
> 
> [1] http://permalink.gmane.org/gmane.comp.emulators.qemu/314406
> 

Thanks for the answers. I think I'm stuck with ARM926, which I think is
not prepared for SMP. I'll have to look if I can use Cortex for my
experiments.

I'll continue interested with the improvements for RT on TCG, but for
the moment I'll go to work on real harware, even though is easier to
run and debug on an emulator.

Thanks
Marc