Re: [PATCH 1/2] sched/fair: expose cpu.max.runtime to set bandwidth runtime directly

[Fernand Sieber <sieberf@amazon.com>]

Hi Tejun,

On Wed, May 27, 2026 at 09:04:37AM -1000, Tejun Heo wrote:
> On Mon, May 25, 2026 at 09:36:21PM +0200, Fernand Sieber wrote:
> > Add a cpu.max.runtime cgroup v2 interface that allows userspace to
> > set the CFS bandwidth controller's runtime directly. This enables
> > CPU credit injection: an orchestrator writes a runtime budget which
> > the cgroup consumes naturally through the existing bandwidth
> > enforcement mechanism.
>
> Can you detail the use case? What problem is it solving how?

Our use case is managing CPU credits for VMs.

Product spec defines credits accumulation rate (quota), credits
limit (burst), and initial level of credits at launch (runtime).

Controlling runtime is also necessary for preserving credits across
live update (kexec) and live migration.

It is possible to approximate this behavior with existing kernel
primitives. However this requires setting up awkward parallel
accounting/control logic from userspace which must be periodically
synced up with the kernel. Instead, we propose minimal changes to
the cpu bw primitives to facilitate this use case.

Thanks.

Fernand



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