From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation Date: Mon, 20 Jun 2011 09:02:30 +0300 Message-ID: <4DFEE276.9020403@redhat.com> References: <1308262856-5779-1-git-send-email-glommer@redhat.com> <1308262856-5779-4-git-send-email-glommer@redhat.com> <4DFDC821.2090905@redhat.com> <4DFEB61A.4070204@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, Rik van Riel , Jeremy Fitzhardinge , Peter Zijlstra , Anthony Liguori , Eric B Munson To: Glauber Costa Return-path: In-Reply-To: <4DFEB61A.4070204@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 06/20/2011 05:53 AM, Glauber Costa wrote: > >> >>> +static void record_steal_time(struct kvm_vcpu *vcpu) >>> +{ >>> + u64 delta; >>> + >>> + if (vcpu->arch.st.stime&& vcpu->arch.st.this_time_out) { >> >> 0 is a valid value for stime. > > > how exactly? stime is a guest physical address... 0 is a valid physical address. >>> >>> @@ -2158,6 +2206,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, >>> int cpu) >>> kvm_migrate_timers(vcpu); >>> vcpu->cpu = cpu; >>> } >>> + >>> + record_steal_time(vcpu); >>> } >> >> This records time spent in userspace in the vcpu thread as steal time. >> Is this what we want? Or just time preempted away? > > There are arguments either way. > > Right now, the way it is, it does account our iothread as steal time, > which is not 100 % accurate if we think steal time as "whatever takes > time away from our VM". I tend to think it as "whatever takes time > away from this CPU", which includes other cpus in the same VM. So > thinking this way, in a 1-1 phys-to-virt cpu mapping, if the iothread > is taking 80 % cpu for whatever reason, we have 80 % steal time the > cpu that is sharing the physical cpu with the iothread. I'm not talking about the iothread, rather the vcpu thread while running in userspace. > > Maybe we could account that as iotime ? > Questions like that are one of the reasons behind me leaving extra > fields in the steal time structure. We could do a more fine grained > accounting and differentiate between the multiple entities that can do > work (of various kinds) in our behalf. > What do other architectures do (xen, s390)? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.