On Wed, 12 Jun 2019 at 09:37, Nadav Amit <nadav.amit@xxxxxxxxx> wrote: > > > 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. Good news, https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=WIP.x86/ipi Thomas who also is the hotplug state machine author introduces shorthands support to native kernel now, I will add the support to kvm_send_ipi_allbutself() and kvm_send_ipi_all() after his work complete. Regards, Wanpeng Li
