From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH] x86: kvm: fix unstable_tsc boot Date: Mon, 24 Feb 2014 18:15:24 -0300 Message-ID: <20140224211524.GC22025@amt.cnet> References: <1393256549-7743-1-git-send-email-drjones@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com To: Andrew Jones Return-path: Content-Disposition: inline In-Reply-To: <1393256549-7743-1-git-send-email-drjones@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Feb 24, 2014 at 04:42:29PM +0100, Andrew Jones wrote: > When the tsc is marked unstable on the host it causes global clock > updates to be requested each time a vcpu is loaded, nearly halting > all progress on guests with a large number of vcpus. > > Fix this by only requesting a local clock update unless the vcpu > is migrating to another cpu. > > Signed-off-by: Andrew Jones > --- > arch/x86/kvm/x86.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 6530019116b0d..ea716a162b4a3 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2781,15 +2781,18 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > vcpu->arch.last_guest_tsc); > kvm_x86_ops->write_tsc_offset(vcpu, offset); > vcpu->arch.tsc_catchup = 1; > + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests); > } > + } > + > + if (unlikely(vcpu->cpu != 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->cpu != cpu) > - kvm_migrate_timers(vcpu); > + kvm_migrate_timers(vcpu); > vcpu->cpu = cpu; > } > > -- > 1.8.1.4 Consider VCPU1 not doing kvm_arch_vcpu_load (guest not executing HLT, not switching VCPUs, no exits to QEMU). VCPU0 doing kvm_arch_vcpu_load (guest executing HLT, say). The updates on VCPU0 must generate updates on VCPU1 as well, otherwise NTP correction applies to VCPU0 but not VCPU1.