> On Jun 10, 2019, at 6:45 PM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > 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. Why do you say so? native_send_call_func_ipi() checks if allbutself shorthand should be used and does so (even though the check can be more efficient - I’m looking at that code right now…)
