| Message ID | 1562376411-3533-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: LAPIC: Implement Exitless Timer | expand |
On 11/07/19 15:50, Wanpeng Li wrote: > kindly ping， Sorry, I need more time to review this. It's basically the only remaining item for the 5.3 merge window, even though it won't be part of the first pull request to Linus. Paolo >> 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. >> >> 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@redhat.com> >> Cc: Radim Krčmář <rkrcmar@redhat.com> >> Cc: Marcelo Tosatti <mtosatti@redhat.com> >> >> v6 -> v7: >> * remove bool argument >> >> v5 -> v6: >> * don't overwrites whatever the user specified >> * introduce kvm_can_post_timer_interrupt and kvm_use_posted_timer_interrupt >> * remove kvm_hlt_in_guest() condition >> * squash all of 2/3/4 together >> >> 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 (2): >> KVM: LAPIC: Make lapic timer unpinned >> KVM: LAPIC: Inject timer interrupt via posted interrupt >> >> arch/x86/kvm/lapic.c | 109 ++++++++++++++++++++++++++-------------- >> arch/x86/kvm/lapic.h | 1 + >> arch/x86/kvm/vmx/vmx.c | 3 +- >> arch/x86/kvm/x86.c | 12 +++-- >> arch/x86/kvm/x86.h | 2 + >> include/linux/sched/isolation.h | 2 + >> kernel/sched/isolation.c | 6 +++ >> 7 files changed, 90 insertions(+), 45 deletions(-) >> >> -- >> 1.8.3.1 >>
On Thu, 11 Jul 2019 at 22:05, Paolo Bonzini <pbonzini@redhat.com> wrote: > > On 11/07/19 15:50, Wanpeng Li wrote: > > kindly ping， > > Sorry, I need more time to review this. It's basically the only > remaining item for the 5.3 merge window, even though it won't be part of > the first pull request to Linus. Thank you! Hope finally we will not miss it. :) Regards, Wanpeng Li
On Sat, 6 Jul 2019 at 09:26, Wanpeng Li <kernellwp@gmail.com> 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. > > 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@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Marcelo Tosatti <mtosatti@redhat.com> > > v6 -> v7: > * remove bool argument > > v5 -> v6: > * don't overwrites whatever the user specified > * introduce kvm_can_post_timer_interrupt and kvm_use_posted_timer_interrupt > * remove kvm_hlt_in_guest() condition > * squash all of 2/3/4 together > > 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 (2): > KVM: LAPIC: Make lapic timer unpinned > KVM: LAPIC: Inject timer interrupt via posted interrupt There is a further optimization for this feature in houseeking/hrtimer subsystem. [1] https://lkml.org/lkml/2019/7/25/963 [2] https://lkml.org/lkml/2019/6/28/231 The [2] patch tries to optimize the worst case, however, it will not be merged by maintainers and get offline confirm, Thomas will refactor this to avoid to predict the future on every timer enqueue. Anyway, it still should be considered to be backported to product environment as long as get_nohz_timer_target() is using. Regards, Wanpeng Li
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. 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@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> v6 -> v7: * remove bool argument v5 -> v6: * don't overwrites whatever the user specified * introduce kvm_can_post_timer_interrupt and kvm_use_posted_timer_interrupt * remove kvm_hlt_in_guest() condition * squash all of 2/3/4 together 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 (2): KVM: LAPIC: Make lapic timer unpinned KVM: LAPIC: Inject timer interrupt via posted interrupt arch/x86/kvm/lapic.c | 109 ++++++++++++++++++++++++++-------------- arch/x86/kvm/lapic.h | 1 + arch/x86/kvm/vmx/vmx.c | 3 +- arch/x86/kvm/x86.c | 12 +++-- arch/x86/kvm/x86.h | 2 + include/linux/sched/isolation.h | 2 + kernel/sched/isolation.c | 6 +++ 7 files changed, 90 insertions(+), 45 deletions(-)