"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes: > Paul Mackerras <paulus@xxxxxxxxx> writes: > >> On Tue, Jun 03, 2014 at 05:46:11PM +0530, Aneesh Kumar K.V wrote: >>> We use time base for PURR and SPURR emulation with PR KVM since we >>> are emulating a single threaded core. When using time base >>> we need to make sure that we don't accumulate time spent in the host >>> in PURR and SPURR value. >> >> Mostly looks good except for this... >> >>> @@ -170,6 +175,11 @@ void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu, >>> >>> out: >>> preempt_enable(); >>> + /* >>> + * Update purr and spurr using time base >>> + */ >>> + vcpu->arch.purr += get_tb() - vcpu->arch.entry_tb; >>> + vcpu->arch.spurr += get_tb() - vcpu->arch.entry_tb; >> >> You need to do those updates before the "out:" label. Otherwise if >> this function gets called with !svcpu->in_use (which can happen if >> CONFIG_PREEMPT is enabled) we would do these updates a second time for >> one guest exit. The thing is that kvmppc_copy_from_svcpu() can get >> called from kvmppc_core_vcpu_put_pr() if the vcpu task gets preempted >> on the way out from the guest before we get to the regular call of >> kvmppc_copy_from_svcpu(). It would then get called again when the >> task gets to run, but this time it does nothing because svcpu->in_use >> is false. > > Looking at the code, since we enable MSR.EE early now, we might possibly > end up calling this function late in the guest exit path. That > implies, we may account that time (time spent after a preempt immediately > following a guest exit) in purr/spurr. I guess that amount of inaccuracy is > ok, because that is the best we could do here ? > May be not, we do call kvmppc_copy_to_svcpu from preempt notifier callbacks. That should ensure that we get the right value. I have sent patch -V2 taking care of the above review comment. -aneesh -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
