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

["Jason J. Herne" <jjherne@linux.vnet.ibm.com>]

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 (jjherne@linux.vnet.ibm.com)