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Re: [PATCH v1 0/2] domctl: Avoid taking domctl lock for certain ops used during migration
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 15 Jun 2026 13:34:12 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 15 Jun 2026 11:34:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.06.2026 13:17, Ross Lagerwall wrote:
> On 6/11/26 5:06 PM, Jan Beulich wrote:
>> On 11.06.2026 18:02, Ross Lagerwall wrote:
>>> On 6/11/26 3:55 PM, Jan Beulich wrote:
>>>> On 09.06.2026 17:15, Ross Lagerwall wrote:
>>>>> When performing multiple migrations in parallel, the domctl lock may
>>>>> become extremely contended:
>>>>>
>>>>> * Operations like "xl vcpu-list" were observed to take in excess of 20s
>>>>> to execute.
>>>>
>>>> Does "xl vcpu-list" involve ...
>>>>
>>>>> * The "clean" shadow op may pause the domain, restart with a
>>>>> continuation and then become blocked on the domctl lock, causing VM
>>>>> downtime in excess of 20 seconds.
>>>>>
>>>>> These issues can be fixed by not holding the domctl for the frequently
>>>>> called operations during migration.
>>>>>
>>>>> Thanks
>>>>>
>>>>> Ross Lagerwall (2):
>>>>> domctl: Handle XEN_DOMCTL_getpageframeinfo3 without the domctl lock
>>>>
>>>> ... XEN_DOMCTL_getpageframeinfo3?
>>>>
>>>
>>> No, but "xl vcpu-list" takes the domctl lock
>>
>> If this is still the case after XSA-492, then maybe the follow-ups I have
>> pending to post will eliminate (or at least reduce) this. I don't think
>> that's 4.22 material, though.
>
> Yes, AFAICT "xl vcpu-list" calls XEN_DOMCTL_getvcpuinfo and
> XEN_DOMCTL_getvcpuaffinity for each domain and both of these still take
> the domctl lock.
XEN_DOMCTL_getvcpuinfo is taken care of by my to-be-posted follow-on.
XEN_DOMCTL_[gs]etvcpuaffinity first need to have their own locking added,
before their handling can be moved out.
Jan
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