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

[Paolo Bonzini]

On 13/07/2015 16:43, Jason J. Herne wrote:
>>>
>>> +    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?
> 
> 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?

Couldn't the iothread starve the VCPUs?  They need to take the iothread
lock in order to process the callbacks.

Paolo