Re: [RFC Patch 0/7] kernel: Introduce multikernel architecture support

[Hillf Danton]

On Mon, 22 Sep 2025 14:55:41 -0700 Cong Wang wrote:
> On Sat, Sep 20, 2025 at 6:47 PM Hillf Danton <hdanton@xxxxxxxx> wrote:
> > On Thu, 18 Sep 2025 15:25:59 -0700 Cong Wang wrote:
> > > This patch series introduces multikernel architecture support, enabling
> > > multiple independent kernel instances to coexist and communicate on a
> > > single physical machine. Each kernel instance can run on dedicated CPU
> > > cores while sharing the underlying hardware resources.
> > >
> > > The multikernel architecture provides several key benefits:
> > > - Improved fault isolation between different workloads
> > > - Enhanced security through kernel-level separation
> > > - Better resource utilization than traditional VM (KVM, Xen etc.)
> > > - Potential zero-down kernel update with KHO (Kernel Hand Over)
> > >
> > Could you illustrate a couple of use cases to help understand your idea?
> 
> Sure, below are a few use cases on my mind:
> 
> 1) With sufficient hardware resources: each kernel gets isolated resources
> with real bare metal performance. This applies to all VM/container use cases
> today, just with pure better performance: no virtualization, no noisy neighbor.
> 
> More importantly, they can co-exist. In theory, you can run a multiernel with
> a VM inside and with a container inside the VM.
> 
If the 6.17 eevdf perfs better than the 6.15 one could, their co-exist wastes
bare metal cpu cycles.

> 2) Active-backup kernel for mission-critical tasks: after the primary kernel
> crashes, a backup kernel in parallel immediately takes over without interrupting
> the user-space task.
> 
> Dual-kernel systems are very common for automotives today.
> 
If 6.17 is more stable than 6.14, running the latter sounds like square skull
in the product environment.

> 3) Getting rid of the OS to reduce the attack surface. We could pack everything
> properly in an initramfs and run it directly without bothering a full
> OS. This is similar to what unikernels or macro VM's do today.
> 
Duno

> 4) Machine learning in the kernel. Machine learning is too specific to
> workloads, for instance, mixing real-time scheduling and non-RT can be challenging for
> ML to tune the CPU scheduler, which is an essential multi-goal learning.
> 
No room for CUDA in kernel I think in 2025.

> 5) Per-application specialized kernel: For example, running a RT kernel
> and non-RT kernel in parallel. Memory footprint can also be reduced by
> reducing the 5-level paging tables when necessary.

If RT makes your product earn more money in fewer weeks, why is eevdf
another option, given RT means no schedule at the first place?