> On Jun 11, 2019, at 3:02 AM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > On Tue, 11 Jun 2019 at 09:48, Nadav Amit <nadav.amit@xxxxxxxxx> wrote: >>> 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…) > > Please continue to follow the apic/x2apic driver. Just apic_flat set > APIC_DEST_ALLBUT/APIC_DEST_ALLINC to ICR. Indeed - I was sure by the name that it does it correctly. That’s stupid. I’ll add it to the patch-set I am working on (TLB shootdown improvements), if you don’t mind.
