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Thu, 09 Apr 2026 07:22:36 -0700 (PDT) From: Lei Chen To: seanjc@google.com Cc: igor@gooddata.com, jan.cipa@gooddata.com, jaroslav.pulchart@gooddata.com, kvm@vger.kernel.org, lei.chen@smartx.com, linux-kernel@vger.kernel.org, pbonzini@redhat.com Subject: [PATCH v2] KVM: x86: Rate-limit global clock updates on vCPU load Date: Thu, 9 Apr 2026 22:22:26 +0800 Message-ID: <20260409142226.2581-1-lei.chen@smartx.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit commit 446fcce2a52b ("Revert "x86: kvm: rate-limit global clock updates"") dropped the rate limiting for KVM_REQ_GLOBAL_CLOCK_UPDATE. As a result, kvm_arch_vcpu_load() can queue global clock update requests every time a vCPU is scheduled when the master clock is disabled or when the vCPU is loaded for the first time. Restore the throttling with a per-VM ratelimit state and gate KVM_REQ_GLOBAL_CLOCK_UPDATE through __ratelimit(), so frequent vCPU scheduling does not generate a steady stream of redundant clock update requests. Fixes: 446fcce2a52b ("Revert "x86: kvm: rate-limit global clock updates"") Signed-off-by: Lei Chen Reported-by: Jaroslav Pulchart Closes: https://lore.kernel.org/all/CAK8fFZ5gY8_Mw2A=iZVFNVKQNrXQzVsn-HTd+Me9K6ZfmdgA+Q@mail.gmail.com/ --- CHANGELOG: v2: - remove comment of kvmclock_update_rs - make sure kvm_arch_vcpu_load make KVM_REQ_CLOCK_UPDATE for this vcpu - add RATELIMIT_MSG_ON_RELEASE to kvmclock_update_rs v1: - initial version(https://lore.kernel.org/all/20260407070046.2336-1-lei.chen@smartx.com/) --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/x86.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 5a3bfa293e8b..5e750c49d21e 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1453,6 +1453,7 @@ struct kvm_arch { bool use_master_clock; u64 master_kernel_ns; u64 master_cycle_now; + struct ratelimit_state kvmclock_update_rs; #ifdef CONFIG_KVM_HYPERV struct kvm_hv hyperv; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 63afdb6bb078..a534e8391611 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5210,8 +5210,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) * On a host with synchronized TSC, there is no need to update * kvmclock on vcpu->cpu migration */ - if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) - kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); + if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) { + if (__ratelimit(&vcpu->kvm->arch.kvmclock_update_rs)) + kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); + else + kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); + } + if (vcpu->cpu != cpu) kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu); vcpu->cpu = cpu; @@ -13189,6 +13194,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) raw_spin_lock_init(&kvm->arch.tsc_write_lock); mutex_init(&kvm->arch.apic_map_lock); seqcount_raw_spinlock_init(&kvm->arch.pvclock_sc, &kvm->arch.tsc_write_lock); + ratelimit_state_init(&kvm->arch.kvmclock_update_rs, HZ, 10); + ratelimit_set_flags(&kvm->arch.kvmclock_update_rs, RATELIMIT_MSG_ON_RELEASE); kvm->arch.kvmclock_offset = -get_kvmclock_base_ns(); raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); -- 2.51.0