Re: [Qemu-devel] [PATCH 3/8] migration: add new capability test-only

["Denis V. Lunev" <den@openvz.org>]

On 10/07/2015 06:05 PM, Eric Blake wrote:
> On 10/07/2015 12:20 AM, Denis V. Lunev wrote:
>> From: Igor Redko <redkoi@virtuozzo.com>
>>
>> This patch declares a new migration capability that allows
>> to distinguish between true migration and the test.
>>
>> An alternative is using a custom URI but in this case the
>> following problems should be solved:
>> 1/ QEMUFile abstraction hides the real transport type
>> 2/ We must be ensured that VM will not be stopped due to
>> “successful migration”
>>
>> Possible solutions:
>> 1/ Using global variable analogous to
>> s->enabled_capabilities[MIGRATION_CAPABILITY_TEST_ONLY] that
>> will be initialized according to the migration type at the
>> beginning of the migration process
>> 2/ Additional hook, presence of implementation of which allows
>> to decide whether the migration is true
>>
> Do we want to name the capability 'x-test-only', since this series is
> experimental, to make it obvious that production code should not rely on it?
>
actually the answer is 'no'. This feature is designated for production.
May be the name is just wrong or description is bad :) Yep, I know this
for sure...

OK. The idea of this feature is to estimate efforts required to
perform migration and downtime during that migration.
This estimate is necessary to decide whether we are able
to automatically move the VM from one node (loaded) to
different node with less load.

Should we rename 'test' to 'estimate' or something like that
to make the situation clearer?

On the other hand this 'estimate' state would be very useful
for testing that is why I have proposed this code to John.
At least we were able to catch recently fixed hang on migration
cancel (in pipeline already).

I am completely open to any idea.


>> +++ b/qapi-schema.json
>> @@ -540,11 +540,14 @@
>>   # @auto-converge: If enabled, QEMU will automatically throttle down the guest
>>   #          to speed up convergence of RAM migration. (since 1.6)
>>   #
>> +# @test-only: If enabled, QEMU instead of migrating will estimate migration
>> +#          time basing on given downtime and current dirty page rate
> If we do decide to add this to mainline, it would need 'since 2.5' (or
> whatever version) documentation.
>
Sure!