> On Jun 11, 2019, at 6:18 PM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > 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. :) Yes, I saw these threads before. But I think the test in native_send_call_func_ipi() should take care of it. I’ll recheck.
