On Wed, 12 Jun 2019 at 00:57, Nadav Amit <nadav.amit@xxxxxxxxx> wrote: > > > 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. Original for hotplug cpu safe. https://lwn.net/Articles/138365/ https://lwn.net/Articles/138368/ Not sure shortcut native support is acceptable, I will play my kvm_send_ipi_allbutself and kvm_send_ipi_all. :) Regards, Wanpeng Li
