Re: cgroup2 freezer and kvm_vm_worker_thread()

[Sean Christopherson <seanjc@google.com>]

On Thu, Nov 07, 2024, Tejun Heo wrote:
> Hello,
> 
> On Thu, Nov 07, 2024 at 07:05:46PM +0100, Michal Koutný wrote:
> ...
> > I'd first ask why the kvm_vm_worker_thread needs to be in the KVM task's
> > cgroup (and copy its priority at creation time but no later adjustments)?
> > 
> > If it can remain inside root cgroup (like any other good kthread) its
> > job may be even chunked into periodic/deferred workqueue pieces with no
> > kthread per KVM at all.
> 
> That'd be better but I suppose kvm wants them in the same cgroup for a
> reason.

Yes.  The one and only user of kvm_vm_create_worker_thread() does non-trivial
work on behalf of the VM, and so we want all of the CPU time consumed by that
work to be charged to the VM's container, e.g. so that a VM that is generating
a lot of work doesn't negatively impact other VMs on the same host (the amount
of work done is directly affected by how the guest is accessing its memory).