Re: [Qemu-devel] [PATCH v4 1/5] cpu: Provide vcpu throttling interface

[Jason J. Herne]

On 07/02/2015 12:43 PM, Paolo Bonzini wrote:
> On 02/07/2015 18:36, Jason J. Herne wrote:
> > +static void cpu_throttle_thread(void *opaque)
> > +{
> > +    double pct = (double)throttle_percentage/100;
> > +    double throttle_ratio = pct / (1 - pct);
> > +    long sleeptime_ms = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE);
> > +
> > +    if (!throttle_percentage) {
> > +        return;
> > +    }
> > +
> > +    qemu_mutex_unlock_iothread();
> > +    g_usleep(sleeptime_ms * 1000); /* Convert ms to us for usleep call */
> > +    qemu_mutex_lock_iothread();
> > +}
> > +
> > +static void cpu_throttle_timer_tick(void *opaque)
> > +{
> > +    CPUState *cpu;
> > +
> > +    /* Stop the timer if needed */
> > +    if (!throttle_percentage) {
> > +        return;
> > +    }
> > +    CPU_FOREACH(cpu) {
> > +        async_run_on_cpu(cpu, cpu_throttle_thread, NULL);
> > +    }
> > +
> > +    timer_mod(throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) +
> > +                                   CPU_THROTTLE_TIMESLICE);
> > +}
>
> This could cause callbacks to pile up I think.  David, do you have any
> idea how to fix it?
>
> Paolo

I'm not sure how callbacks can pile up here. If the vcpus are running 
then their thread's will execute the callbacks. If they are not running 
then the use of QEMU_CLOCK_VIRTUAL_RT will prevent the callbacks from 
stacking because the timer is not running, right?


--
-- Jason J. Herne (address@hidden)