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Re: [PATCH v1 0/2] domctl: Avoid taking domctl lock for certain ops used during migration
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Mon, 15 Jun 2026 12:17:59 +0100
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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 11:18:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Ross
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