Messages in this thread | | | Date | Wed, 6 Sep 2023 14:40:59 +0800 | Subject | Re: [PATCH] KVM: X86: Reduce calls to vcpu_load | From | Xiaoyao Li <> |
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On 9/6/2023 2:24 PM, Hao Peng wrote: > From: Peng Hao <flyingpeng@tencent.com> > > The call of vcpu_load/put takes about 1-2us. Each > kvm_arch_vcpu_create will call vcpu_load/put > to initialize some fields of vmcs, which can be > delayed until the call of vcpu_ioctl to process > this part of the vmcs field, which can reduce calls > to vcpu_load.
what if no vcpu ioctl is called after vcpu creation?
And will the first (it was second before this patch) vcpu_load() becomes longer? have you measured it?
I don't think it worth the optimization unless a strong reason.
> Signed-off-by: Peng Hao <flyingpeng@tencent.com> > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/x86.c | 21 ++++++++++++++++----- > 2 files changed, 17 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 9320019708f9..2f2dcd283788 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -984,6 +984,7 @@ struct kvm_vcpu_arch { > /* Flush the L1 Data cache for L1TF mitigation on VMENTER */ > bool l1tf_flush_l1d; > > + bool initialized; > /* Host CPU on which VM-entry was most recently attempted */ > int last_vmentry_cpu; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4fd08a5e0e98..a3671a54e850 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -317,7 +317,20 @@ const struct kvm_stats_header kvm_vcpu_stats_header = { > u64 __read_mostly host_xcr0; > > static struct kmem_cache *x86_emulator_cache; > +static int kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz); > > +static inline bool kvm_vcpu_initialized(struct kvm_vcpu *vcpu) > +{ > + return vcpu->arch.initialized; > +} > + > +static void kvm_vcpu_initial_reset(struct kvm_vcpu *vcpu) > +{ > + kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz); > + kvm_vcpu_reset(vcpu, false); > + kvm_init_mmu(vcpu); > + vcpu->arch.initialized = true; > +} > /* > * When called, it means the previous get/set msr reached an invalid msr. > * Return true if we want to ignore/silent this failed msr access. > @@ -5647,6 +5660,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > > vcpu_load(vcpu); > > + if (!kvm_vcpu_initialized(vcpu)) > + kvm_vcpu_initial_reset(vcpu); > + > u.buffer = NULL; > switch (ioctl) { > case KVM_GET_LAPIC: { > @@ -11930,11 +11946,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) > vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT; > kvm_xen_init_vcpu(vcpu); > kvm_vcpu_mtrr_init(vcpu); > - vcpu_load(vcpu); > - kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz); > - kvm_vcpu_reset(vcpu, false); > - kvm_init_mmu(vcpu); > - vcpu_put(vcpu); > return 0; > > free_guest_fpu: > -- > 2.31.1
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