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 Krčmář 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
