On 6/6/19 7:36 PM, Andrea Arcangeli wrote: > Hello, > > On Thu, Jun 06, 2019 at 07:25:28PM +0100, Joao Martins wrote: >> But I wonder whether we should fail to load cpuidle-haltpoll when host halt >> polling can't be disabled[*]? That is to avoid polling in both host and guest >> and *possibly* avoid chances for performance regressions when running on older >> hypervisors? > > I don't think it's necessary: that would force an upgrade of the host > KVM version in order to use the guest haltpoll feature with an > upgraded guest kernel that can use the guest haltpoll. > Hence why I was suggesting a *guest* cpuidle-haltpoll module parameter to still allow it to load or otherwise (or allow guest to pick). > The guest haltpoll is self contained in the guest, so there's no > reason to prevent that by design or to force upgrade of the KVM host > version. It'd be more than enough to reload kvm.ko in the host with > the host haltpoll set to zero with the module parameter already > available, to achieve the same runtime without requiring a forced host > upgrade. > It's just with the new driver we unilaterally poll on both sides, just felt I would point it out should this raise unattended performance side effects ;) > The warning however sounds sensible. > Cool. Joao
