Re: [Qemu-devel] [RFC PATCH V7 09/19] Drop global lock during TCG code execution

[Frederic Konrad]

On 12/08/2015 11:58, Paolo Bonzini wrote:
> On 11/08/2015 23:34, Frederic Konrad wrote:
> > > Also if qemu_cond_broadcast(&qemu_io_proceeded_cond) is being dropped
> > > there is no point keeping the guff around in qemu_tcg_wait_io_event.
> > Yes good point.
> >
> > BTW this leads to high consumption of host CPU eg: 100% per VCPU thread as
> > the VCPUs thread are no longer waiting for qemu_io_proceeded_cond.
> If the guest CPU is busy waiting, that's expected.  But if the guest CPU
> is halted, it should not have 100% host CPU consumption.
>
> Paolo
Hmm so that's definitely strange... I mean theorically it's the same as 
before?

An other thing. It seems that we need to signal the VCPU when the 
iothread take
the lock eg:

    if (tcg_enabled() && qemu_thread_is_self(&io_thread)) {
        CPU_FOREACH(cpu) {
            cpu_exit(cpu);
        }
    }

To make this patch working without MTTCG.

Fred