Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary

[Wanpeng Li]

On Tue, 11 Jun 2019 at 09:11, Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Mon, Jun 10, 2019 at 04:34:20PM +0200, Radim KrÄmÃÅ wrote:
> > 2019-05-30 09:05+0800, Wanpeng Li:
> > > The idea is from Xen, when sending a call-function IPI-many to vCPUs,
> > > yield if any of the IPI target vCPUs was preempted. 17% performance
> > > increasement of ebizzy benchmark can be observed in an over-subscribe
> > > environment. (w/ kvm-pv-tlb disabled, testing TLB flush call-function
> > > IPI-many since call-function is not easy to be trigged by userspace
> > > workload).
> >
> > Have you checked if we could gain performance by having the yield as an
> > extension to our PV IPI call?
> >
> > It would allow us to skip the VM entry/exit overhead on the caller.
> > (The benefit of that might be negligible and it also poses a
> >  complication when splitting the target mask into several PV IPI
> >  hypercalls.)
>
> Tangetially related to splitting PV IPI hypercalls, are there any major
> hurdles to supporting shorthand?  Not having to generate the mask for
> ->send_IPI_allbutself and ->kvm_send_ipi_all seems like an easy to way
> shave cycles for affected flows.

Not sure why shorthand is not used for native x2apic mode.

Regards,
Wanpeng Li