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

[Chegu Vinod <chegu_vinod@hp.com>]

On 4/30/2013 9:01 AM, Juan Quintela wrote:
> 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

I tend to agree.

For now I am not going to hold the iothread lock for following the list...

> (it is not working well anyways as
> Today).

Yes...and I see that Igor, Eduardo et.al. are trying to fix this.

Vinod

>
> Thanks,  Juan.
> .
>