Re: [Qemu-devel] [RFC PATCH v2] Throttle-down guest when live migration does not converge.

[Juan Quintela <quintela@redhat.com>]

Chegu Vinod <chegu_vinod@hp.com> wrote:
> On 4/30/2013 8:20 AM, Juan Quintela wrote:
>>>
>>> (qemu) info migrate
>>> capabilities: xbzrle: off auto-converge: off  <----
>>> Migration status: active
>>> total time: 1487503 milliseconds
>> 148 seconds
>
> 1487 seconds and still the Migration is not completed.
>
>>
>>> expected downtime: 519 milliseconds
>>> transferred ram: 383749347 kbytes
>>> remaining ram: 2753372 kbytes
>>> total ram: 268444224 kbytes
>>> duplicate: 65461532 pages
>>> skipped: 64901568 pages
>>> normal: 95750218 pages
>>> normal bytes: 383000872 kbytes
>>> dirty pages rate: 67551 pages
>>>
>>> ---
>>>
>>> (qemu) info migrate
>>> capabilities: xbzrle: off auto-converge: on   <----
>>> Migration status: completed
>>> total time: 241161 milliseconds
>>> downtime: 6373 milliseconds
>> 6.3 seconds and finished,  not bad at all O:-)
> That's the *downtime*..  The total time for migration to complete is
> 241 secs. (SpecJBB is
> one of those workloads that dirties memory quite a bit).

Sorry,  you are right.  Imressive anyways for such small change.

>>> +/* To reduce the dirty rate explicitly disallow the VCPUs from spending
>>> +   much time in the VM. The migration thread will try to catchup.
>>> +   Workload will experience a greater performance drop but for a shorter
>>> +   duration.
>>> +*/
>>> +void *migration_throttle_down(void *opaque)
>>> +{
>>> +    throttling = true;
>>> +    while (throttling_needed()) {
>>> +        CPUArchState *penv = first_cpu;
>> I am not sure that we can follow the list without the iothread lock
>> here.
>
> Hmm.. Is this due to vcpu hot plug that might happen at the time of
> live migration (or) due
> to something else ? I was trying to avoid holding the iothread lock
> for longer duration and slow
> down the migration thread...

Well,  thinking back about it,  what we should do is disable cpu
hotplug/unplug during migration (it is not working well anyways as
Today).

Thanks,  Juan.