On Fri, 28 Jun 2019 at 17:12, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > 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. Hmm, should fallback to native shorthands when support. Regards, Wanpeng Li
