Re: [Xen-devel] [xen-unstable test] 128240: regressions - FAIL

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/10/18 16:35, Wei Liu wrote:
> On Mon, Oct 01, 2018 at 04:19:07PM +0100, George Dunlap wrote:
>> On 10/01/2018 04:17 PM, Wei Liu wrote:
>>> On Mon, Oct 01, 2018 at 09:10:25AM -0600, Jan Beulich wrote:
>>>>>>> On 01.10.18 at 16:33, <wei.liu2@xxxxxxxxxx> wrote:
>>>>> On Mon, Oct 01, 2018 at 03:04:02AM -0600, Jan Beulich wrote:
>>>>>>>>> On 30.09.18 at 23:59, <osstest-admin@xxxxxxxxxxxxxx> wrote:
>>>>>>> flight 128240 xen-unstable real [real]
>>>>>>> http://logs.test-lab.xenproject.org/osstest/logs/128240/ 
>>>>>>>
>>>>>>> Regressions :-(
>>>>>>>
>>>>>>> Tests which did not succeed and are blocking,
>>>>>>> including tests which could not be run:
>>>>>>>  test-amd64-amd64-migrupgrade 22 guest-migrate/src_host/dst_host fail 
>>>>>>> REGR. vs. 
>>>>> 128084
>>>>>> At the first glance
>>>>>>
>>>>>> libxl: error: libxl_sched.c:232:sched_credit_domain_set: Domain 
>>>>>> 1:Getting 
>>>>> domain sched credit: Invalid argument
>>>>>> libxl: error: libxl_create.c:1275:domcreate_rebuild_done: Domain 
>>>>>> 1:cannot 
>>>>> (re-)build domain: -3
>>>>>> might indicate a problem resulting from the switch to credit2 as the 
>>>>>> default
>>>>>> scheduler. But "first glance" here really means what it says - I didn't 
>>>>>> look
>>>>>> (yet) at what exactly libxl tries to do there, in the hope that others 
>>>>>> may
>>>>>> know without much digging.
>>>>> I think this is due to toolstack trying to set the same scheduler
>>>>> parameters for the newly created guest.
>>>>>
>>>>> But in this test, the destination host is using a different scheduler
>>>>> from the source host. Asking for credit scheduler on a credit2 host is
>>>>> wrong.
>>>>>
>>>>> The relevant snippet in guest cfg (JSON) is:
>>>>>
>>>>>                 "sched_params": {
>>>>>                     "sched": "credit",
>>>>>                     "weight": 256,
>>>>>                     "cap": 0
>>>>>                 },
>>>>>
>>>>> I can't think of a method to fix it off the top of my head though.
>>>> So is this something that was specified in the original config? Or
>>>> is it just the current value which gets read and an attempt made
>>>> to re-install. If there was no explicit setting in the guest config,
>>>> shouldn't such a "default" setting be retained by not transferring
>>>> any scheduler specifics during migration?
>>>>
>>> No setting in guest cfg. Those values are extracted from the hypervisor.
>>> I think we may be able to not send default values to the remote end.
>> Wait, the migration code reads the scheduler parameters -- even if these
>> have not been explicitly set by the admin -- and sends them along with
>> the migration stream?  And if the remote scheduler is different, the
>> migration fails?
>>
>> That's not so good. :-)
> But one can argue that the guest is specific configured that way so it's
> parameters should be preserved. We normally analyse things on a case by
> case basis.

If there isn't an obvious fix, then the switch of default scheduler
needs reverting until there is a fix present.  This is currently
blocking master.

~Andrew

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