Re: [Qemu-devel] [PATCH v11 14/15] rdma: introduce MIG_STATE_NONE and change MIG_STATE_SETUP state transition

["Michael R. Hines" <mrhines@linux.vnet.ibm.com>]

On 06/25/2013 06:13 AM, Paolo Bonzini wrote:
> Il 25/06/2013 11:49, Juan Quintela ha scritto:
>> mrhines@linux.vnet.ibm.com wrote:
>>> From: "Michael R. Hines" <mrhines@us.ibm.com>
>>>
>>> As described in the previous patch, until now, the MIG_STATE_SETUP
>>> state was not really a 'formal' state. It has been used as a 'zero' state
>>> (what we're calling 'NONE' here) and QEMU has been unconditionally transitioning
>>> into this state when the QMP migration command was called. Instead we want to
>>> introduce MIG_STATE_NONE, which is our starting state in the state machine, and
>>> then immediately transition into the MIG_STATE_SETUP state when the QMP migrate
>>> command is issued.
>>>
>>> In order to do this, we must delay the transition into MIG_STATE_ACTIVE until
>>> later in the migration_thread(). This is done to be able to timestamp the amount of
>>> time spent in the SETUP state for proper accounting to the user during
>>> an RDMA migration.
>>>
>>> Furthermore, the management software, until now, has never been aware of the
>>> existence of the SETUP state whatsoever. This must change, because, timing of this
>>> state implies that the state actually exists.
>>>
>>> These two patches cannot be separated because the 'query_migrate' QMP
>>> switch statement needs to know how to handle this new state transition.
>>>
>>> Tested-by: Michael R. Hines <mrhines@us.ibm.com>
>>> Signed-off-by: Michael R. Hines <mrhines@us.ibm.com>
>>> @@ -316,6 +321,7 @@ static void migrate_fd_cancel(MigrationState *s)
>>>   {
>>>       DPRINTF("cancelling migration\n");
>>>   
>>> +    migrate_set_state(s, MIG_STATE_SETUP, MIG_STATE_CANCELLED);
>>>       migrate_set_state(s, MIG_STATE_ACTIVE, MIG_STATE_CANCELLED);
>>>   }
>> This chunk is wrong.
>>
>> we can call qme_migrate_cancel() at any point,  and it is going to be
>> called normally from MIG_STATE_ACTIVE.
>>
>>      migrate_set_satet(s, s->state,  MIG_STATE_CANCELLED)
>>
>> should do the trick.  Or something like that,  what do you think?
> I don't like the three-arguments migrate_set_state, but I don't have any
> better idea.
>
> With Juan's modification, it is fine (but not reviewed-by me :)).  While
> you resend, the first 13 patches of v10 can be merged (pull request).
> You can then rebase the last three on top.

So, I should send a v11 before Juan applies and generates the pull request?

Did I understand correctly?

> Michael, did you look at the "debugging/getting the protocol ready" mode
> where all pages are unpinned?
>
> Paolo
>


We did not come up with a design on how such a mode would be
exposed to the user. Implementing this in migration-rdma.c is
just a few lines of code, but without a clear use case in this patch
series, I've not chosen expose it to the user yet without some kind
of agreement with you guys.

Recommendations?