From: David Woodhouse Date: Sun, 28 Apr 2024 12:59:49 +0000 (+0100) Subject: KVM: x86: Avoid gratuitous global clock reload in kvm_arch_vcpu_load() X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=e3105770a46661e5dc8db4f3afb801a1bc6d9eb2;p=users%2Fdwmw2%2Flinux.git KVM: x86: Avoid gratuitous global clock reload in kvm_arch_vcpu_load() Commit d98d07ca7e034 ("KVM: x86: update pvclock area conditionally, on cpu migration") turned an unconditional KVM_REQ_CLOCK_UPDATE into a conditional one, if either the master clock isn't enabled *or* the vCPU was not previously scheduled (vcpu->cpu == -1). The commit message doesn't explain the latter condition, which is specifically for the master clock case. Commit 0061d53daf26f ("KVM: x86: limit difference between kvmclock updates") later turned that into a KVM_REQ_GLOBAL_CLOCK_UPDATE to avoid skew between vCPUs. In master clock mode there is no need for any of that, regardless of whether/where this vCPU was previously scheduled. Do it only if (!kvm->arch.use_master_clock). Signed-off-by: David Woodhouse --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 32a873d5ed006..dd53860ca2845 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5161,7 +5161,7 @@ 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) + if (!vcpu->kvm->arch.use_master_clock) kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); if (vcpu->cpu != cpu) kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu);