On Tue, Jun 11, 2019 at 08:17:07PM +0800, Wanpeng Li wrote: > From: Wanpeng Li <[email protected]> > > Dedicated instances are currently disturbed by unnecessary jitter due > to the emulated lapic timers fire on the same pCPUs which vCPUs resident. > There is no hardware virtual timer on Intel for guest like ARM. Both > programming timer in guest and the emulated timer fires incur vmexits. > This patch tries to avoid vmexit which is incurred by the emulated > timer fires in dedicated instance scenario. > > When nohz_full is enabled in dedicated instances scenario, the emulated > timers can be offload to the nearest busy housekeeping cpus since APICv > is really common in recent years. The guest timer interrupt is injected > by posted-interrupt which is delivered by housekeeping cpu once the emulated > timer fires. > > ~3% redis performance benefit can be observed on Skylake server. > > w/o patch: > > VM-EXIT Samples Samples% Time% Min Time Max Time Avg time > > EXTERNAL_INTERRUPT 42916 49.43% 39.30% 0.47us 106.09us 0.71us ( > +- 1.09% ) > > w/ patch: > > VM-EXIT Samples Samples% Time% Min Time Max Time > Avg time > > EXTERNAL_INTERRUPT 6871 9.29% 2.96% 0.44us 57.88us 0.72us ( > +- 4.02% ) > > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]> > --- > arch/x86/kvm/lapic.c | 32 +++++++++++++++++++++++++------- > 1 file changed, 25 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index e57eeba..020599f 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -133,6 +133,12 @@ inline bool posted_interrupt_inject_timer_enabled(struct > kvm_vcpu *vcpu) > } > EXPORT_SYMBOL_GPL(posted_interrupt_inject_timer_enabled); > > +static inline bool can_posted_interrupt_inject_timer(struct kvm_vcpu *vcpu) > +{ > + return posted_interrupt_inject_timer_enabled(vcpu) && > + kvm_hlt_in_guest(vcpu->kvm); > +}
Hi Li, Don't think its necessary to depend on kvm_hlt_in_guest: Can also use exitless injection if the guest is running (think DPDK style workloads that busy-spin on network card).
