Re: [RFC PATCH v1 0/2] Avoid rcu_core() if CPU just left guest vcpu

Leonardo Bras
2024-05-11T02:08:51Z

On Wed, May 08, 2024 at 07:01:29AM -0700, Sean Christopherson wrote:
> On Wed, May 08, 2024, Leonardo Bras wrote:
> > Something just hit me, and maybe I need to propose something more generic.
>
> Yes. This is what I was trying to get across with my complaints about keying off
> of the last VM-Exit time. It's effectively a broad stroke "this task will likely
> be quiescent soon" and so the core concept/functionality belongs in common code,
> not KVM.
>

Hello Sean,

Paul implemented the RCU patience cmdline option, that will help avoiding
rcuc waking up if the grace period is younger than X miliseconds, which
means the last quiescent state needs to be at least X miliseconds old.

With that I just have to add a quiescent state in guest_exit(), and we will
be able to get the same effect of last_guest_exit patch.

I sent this RFC patch doing that:
https://lore.kernel.org/all/20240511020557.1198200-1-leobras@redhat.com/

Please take a look.

Thanks!
Leo