From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] allow userspace to adjust kvmclock offset Date: Mon, 12 Oct 2009 10:53:26 +0200 Message-ID: <4AD2EE86.50807@redhat.com> References: <1254849896-3947-1-git-send-email-glommer@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Glauber Costa Return-path: In-Reply-To: <1254849896-3947-1-git-send-email-glommer@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 10/06/2009 07:24 PM, Glauber Costa wrote: > When we migrate a kvm guest that uses pvclock between two hosts, we may > suffer a large skew. This is because there can be significant differences > between the monotonic clock of the hosts involved. When a new host with > a much larger monotonic time starts running the guest, the view of time > will be significantly impacted. > > Situation is much worse when we do the opposite, and migrate to a host with > a smaller monotonic clock. > > This new proposed ioctl will allow userspace to inform us what is the monotonic > clock value in the source host, so we can keep the time skew short, and more > importantly, never goes backwards. > > > diff --git a/include/linux/kvm.h b/include/linux/kvm.h > index f8f8900..0cd5ad8 100644 > --- a/include/linux/kvm.h > +++ b/include/linux/kvm.h > @@ -546,6 +546,7 @@ struct kvm_irqfd { > #define KVM_CREATE_PIT2 _IOW(KVMIO, 0x77, struct kvm_pit_config) > #define KVM_SET_BOOT_CPU_ID _IO(KVMIO, 0x78) > #define KVM_IOEVENTFD _IOW(KVMIO, 0x79, struct kvm_ioeventfd) > +#define KVM_ADJUST_CLOCK _IOW(KVMIO, 0x7a, __u64) > Please change to a struct with some reserved space. Do we want an absolute or relative adjustment? -- error compiling committee.c: too many arguments to function