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

[Frederic Konrad]

On 11/08/2015 22:12, Alex Bennée wrote:
> Paolo Bonzini <address@hidden> writes:
>
> > On 10/08/2015 17:27, address@hidden wrote:
> > >   void qemu_mutex_lock_iothread(void)
> > >   {
> > > -    atomic_inc(&iothread_requesting_mutex);
> > > -    /* In the simple case there is no need to bump the VCPU thread out of
> > > -     * TCG code execution.
> > > -     */
> > > -    if (!tcg_enabled() || qemu_in_vcpu_thread() ||
> > > -        !first_cpu || !first_cpu->thread) {
> > > -        qemu_mutex_lock(&qemu_global_mutex);
> > > -        atomic_dec(&iothread_requesting_mutex);
> > > -    } else {
> > > -        if (qemu_mutex_trylock(&qemu_global_mutex)) {
> > > -            qemu_cpu_kick_thread(first_cpu);
> > > -            qemu_mutex_lock(&qemu_global_mutex);
> > > -        }
> > > -        atomic_dec(&iothread_requesting_mutex);
> > > -        qemu_cond_broadcast(&qemu_io_proceeded_cond);
> > > -    }
> > > -    iothread_locked = true;
> > "iothread_locked = true" must be kept.  Otherwise... yay! :)
> 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.

Fred