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

From: Radim KrÄmÃÅ
Date: Mon Jun 10 2019 - 10:38:47 EST

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