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. Regards, Wanpeng Li
