Messages in this thread | | | Date | Mon, 20 Jun 2011 09:02:30 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation |
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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.
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