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?
Thanks,
Paolo
> w/o patchset:
>
> 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/ patchset:
>
> 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 <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> v4 -> v5:
> * update patch description in patch 1/4
> * feed latest apic->lapic_timer.expired_tscdeadline to kvm_wait_lapic_expire()
> * squash advance timer handling to patch 2/4
>
> v3 -> v4:
> * drop the HRTIMER_MODE_ABS_PINNED, add kick after set pending timer
> * don't posted inject already-expired timer
>
> v2 -> v3:
> * disarming the vmx preemption timer when posted_interrupt_inject_timer_enabled()
> * check kvm_hlt_in_guest instead
>
> v1 -> v2:
> * check vcpu_halt_in_guest
> * move module parameter from kvm-intel to kvm
> * add housekeeping_enabled
> * rename apic_timer_expired_pi to kvm_apic_inject_pending_timer_irqs
>
>
> Wanpeng Li (4):
> KVM: LAPIC: Make lapic timer unpinned
> KVM: LAPIC: Inject timer interrupt via posted interrupt
> KVM: LAPIC: Ignore timer migration when lapic timer is injected by pi
> KVM: LAPIC: Don't inject already-expired timer via posted interrupt
>
> arch/x86/kvm/lapic.c | 68 +++++++++++++++++++++++++++--------------
> arch/x86/kvm/lapic.h | 3 +-
> arch/x86/kvm/svm.c | 2 +-
> arch/x86/kvm/vmx/vmx.c | 5 +--
> arch/x86/kvm/x86.c | 11 ++++---
> arch/x86/kvm/x86.h | 2 ++
> include/linux/sched/isolation.h | 2 ++
> kernel/sched/isolation.c | 6 ++++
> 8 files changed, 67 insertions(+), 32 deletions(-)
>
