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

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

On 07/31/2015 01:16 PM, Paolo Bonzini wrote:
>
>
> On 31/07/2015 19:12, Jason J. Herne wrote:
>>>
>>>
>>
>> Throttle ratio is relative to CPU_THROTTLE_TIMESLICE. Take a look at how
>> throttle_ratio is used in the calculation:
>>
>> long sleeptime_ms = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE);
>>
>> A value of 1 means we sleep the same amount of time that we execute.
>
> But that doesn't work if your timer runs every CPU_THROTTLE_TIMESLICE
> milliseconds, and thus schedules async work every CPU_THROTTLE_TIMESLICE
> milliseconds.
>
> The timer would have to be scheduled every (throttle_ratio + 1) *
> CPU_THROTTLE_TIMESLICE milliseconds, i.e. CPU_THROTTLE_TIMESLICE /
> (1-pct) milliseconds.
>
> Paolo

Doh! Yep :). This problem is an artifact of moving the timer_mod from
cpu_throttle_thread into cpu_throttle_timer_tick. I'll have to go back
to the review comments and look at why that was done.

-- 
-- Jason J. Herne (jjherne@linux.vnet.ibm.com)