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Fri, 23 Aug 2024 05:25:29 +0000 Date: Fri, 23 Aug 2024 13:25:18 +0800 From: Chao Gao To: Suleiman Souhlal CC: Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , , , Subject: Re: [PATCH v2 2/3] KVM: x86: Include host suspended time in steal time. 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This can be particularly noticeable >> >if the guest task was RT, as it can end up getting throttled for a >> >long time. >> > >> >To mitigate this issue, we include the time that the host was >> >suspended in steal time, which lets the guest subtract the duration from >> >the tasks' runtime. >> > >> >Note that the case of a suspend happening during a VM migration >> >might not be accounted. >> > >> >Signed-off-by: Suleiman Souhlal >> >--- >> > arch/x86/include/asm/kvm_host.h | 1 + >> > arch/x86/kvm/x86.c | 11 ++++++++++- >> > 2 files changed, 11 insertions(+), 1 deletion(-) >> > >> >diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> >index 4a68cb3eba78f8..728798decb6d12 100644 >> >--- a/arch/x86/include/asm/kvm_host.h >> >+++ b/arch/x86/include/asm/kvm_host.h >> >@@ -898,6 +898,7 @@ struct kvm_vcpu_arch { >> > u8 preempted; >> > u64 msr_val; >> > u64 last_steal; >> >+ u64 last_suspend_ns; >> > struct gfn_to_hva_cache cache; >> > } st; >> > >> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> >index 70219e4069874a..104f3d318026fa 100644 >> >--- a/arch/x86/kvm/x86.c >> >+++ b/arch/x86/kvm/x86.c >> >@@ -3654,7 +3654,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu) >> > struct kvm_steal_time __user *st; >> > struct kvm_memslots *slots; >> > gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS; >> >- u64 steal; >> >+ u64 steal, suspend_ns; >> > u32 version; >> > >> > if (kvm_xen_msr_enabled(vcpu->kvm)) { >> >@@ -3735,6 +3735,14 @@ static void record_steal_time(struct kvm_vcpu *vcpu) >> > steal += current->sched_info.run_delay - >> > vcpu->arch.st.last_steal; >> > vcpu->arch.st.last_steal = current->sched_info.run_delay; >> >+ /* >> >+ * Include the time that the host was suspended in steal time. >> >+ * Note that the case of a suspend happening during a VM migration >> >+ * might not be accounted. >> >+ */ >> >+ suspend_ns = kvm_total_suspend_ns(); >> >+ steal += suspend_ns - vcpu->arch.st.last_suspend_ns; >> >+ vcpu->arch.st.last_suspend_ns = suspend_ns; >> >> The document in patch 3 states: >> >> Time during which the vcpu is idle, will not be reported as steal time >> >> I'm wondering if all host suspend time should be reported as steal time, >> or if the suspend time during a vCPU halt should be excluded. > >I think the statement about idle time not being reported as steal isn't >completely accurate, so I'm not sure if it's worth the extra complexity. > >> >> > unsafe_put_user(steal, &st->steal, out); >> > >> > version += 1; >> >@@ -12280,6 +12288,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) >> > >> > vcpu->arch.arch_capabilities = kvm_get_arch_capabilities(); >> > vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT; >> >+ vcpu->arch.st.last_suspend_ns = kvm_total_suspend_ns(); >> >> is this necessary? I doubt this because KVM doesn't capture >> current->sched_info.run_delay here. > >Isn't run_delay being captured by the scheduler at all time? I meant KVM doesn't do: vcpu->arch.st.last_steal = current->sched_info.run_delay; at vCPU creation time. > >We need to initialize last_suspend_ns otherwise the first call to >record_steal_time() for a VCPU would report a wrong value if >the VCPU is started after the host has already had a suspend. But initializing last_suspend_ns here doesn't guarantee KVM won't report a "wrong" value because a suspend can happen after vCPU creation and before its first VM-enter.