Re: [Xen-devel] [PATCH v11]xen: sched: convert RTDS from time to event driven model

[Meng Xu <xumengpanda@xxxxxxxxx>]

>> > I tried to create a cpupool and then migrate a VM to the new
>> > cpupool;
>>
> BTW, Meng:
>
> (XEN)    [<ffff82d08012e182>] schedule_cpu_switch+0x250/0x28a
> (XEN)    [<ffff82d080101b49>] cpupool.c#cpupool_assign_cpu_locked+0x31/0x11f
>
> I think you mean "and then move a CPU from a cpupool to another". Or
> perhaps what you said is what your script does, and you weren't sure at
> what stage it explodes.
>
> Well, let me tell you: it's when you move a CPU between pools that have
> schedulers that remaps the scheduler locks (such as Credit2-->RTDS and
> vice versa).

Thanks Dario for the explanation!
Yes, I looked into the cpu_switch things before and found the bug is
triggered by the lock remapping.

>
>> > However, the system triggers the bug as below. I guess this is some
>> > kind of bug that are known to us,  and Dario had some uncommitted
>> > patch to fix it, IIRC?
>> In the context of this patch the most relevant question is: Is this
>> an issue with the patch, or one that existed already before?
>>
> Exactly!
>
> And the answer is:
>  - it's pre-existing
>  - it's an even bigger issue than that ASSERT triggering (i.e., there
>    are potential races even when things works)

Ah-ha, I didn't know this before. :-)

>  - I'm taking care of it.

Thank you so much! I'm looking forward to it. :-D

Thanks and Best Regards,

Meng

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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