On Tue, Jul 02, 2019 at 06:38:56PM +0200, Paolo Bonzini wrote:
> On 21/06/19 11:39, Wanpeng Li wrote:
> > 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 patchset 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 unpinned
> > timer will be moved to the nearest busy housekeepers after commit
> > 9642d18eee2cd (nohz: Affine unpinned timers to housekeepers) and commit
> > 444969223c8 ("sched/nohz: Fix affine unpinned timers mess"). However,
> > KVM always makes lapic timer pinned to the pCPU which vCPU residents, the
> > reason is explained by commit 61abdbe0 (kvm: x86: make lapic hrtimer
> > pinned). Actually, these emulated timers can be offload to the 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.
> >
> > The host admin should fine tuned, e.g. dedicated instances scenario w/
> > nohz_full cover the pCPUs which vCPUs resident, several pCPUs surplus
> > for busy housekeeping, disable mwait/hlt/pause vmexits to keep in non-root
> > mode, ~3% redis performance benefit can be observed on Skylake server.
>
> Marcelo,
>
> does this patch work for you or can you still see the oops?
Hi Paolo,
No more oopses with kvm/queue. Can you include:
Index: kvm/arch/x86/kvm/lapic.c
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.c
+++ kvm/arch/x86/kvm/lapic.c
@@ -124,8 +124,7 @@ static inline u32 kvm_x2apic_id(struct k
bool posted_interrupt_inject_timer(struct kvm_vcpu *vcpu)
{
- return pi_inject_timer && kvm_vcpu_apicv_active(vcpu) &&
- kvm_hlt_in_guest(vcpu->kvm);
+ return pi_inject_timer && kvm_vcpu_apicv_active(vcpu);
}
EXPORT_SYMBOL_GPL(posted_interrupt_inject_timer);
However, for some reason (hrtimer subsystems responsability) with cyclictest -i
200
on the guest, the timer runs on the local CPU:
CPU 1/KVM-9454 [003] d..2 881.674196: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674200: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d.h. 881.674387: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 881.674393: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674395: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674399: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d.h. 881.674586: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 881.674593: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674595: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674599: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d.h. 881.674787: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 881.674793: get_nohz_timer_target:
get_nohz_timer_target 3->0
CPU 1/KVM-9454 [003] d..2 881.674795: get_nohz_timer_target:
get_nohz_timer_target 3->0
But on boot:
CPU 1/KVM-9454 [003] d..2 578.625394: get_nohz_timer_target:
get_nohz_timer_target 3->0
<idle>-0 [000] d.h1 578.626390: apic_timer_fn
<-__hrtimer_run_queues
<idle>-0 [000] d.h1 578.626394:
apic_timer_fn<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 578.626401: get_nohz_timer_target:
get_nohz_timer_target 3->0
<idle>-0 [000] d.h1 578.628397: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 578.628407: get_nohz_timer_target:
get_nohz_timer_target 3->0
<idle>-0 [000] d.h1 578.631403: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 578.631413: get_nohz_timer_target:
get_nohz_timer_target 3->0
<idle>-0 [000] d.h1 578.635409: apic_timer_fn
<-__hrtimer_run_queues
CPU 1/KVM-9454 [003] d..2 578.635419: get_nohz_timer_target:
get_nohz_timer_target 3->0
<idle>-0 [000] d.h1 578.640415: apic_timer_fn
<-__hrtimer_run_queues
Thanks.
