2016-07-07 17:42 GMT+08:00 Peter Zijlstra <peterz@xxxxxxxxxxxxx>: > On Thu, Jul 07, 2016 at 04:48:05PM +0800, Wanpeng Li wrote: >> 2016-07-06 20:28 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >> > Hmm, you're right. We can use bit 0 of struct kvm_steal_time's flags to >> > indicate that pad[0] is a "VCPU preempted" field; if pad[0] is 1, the >> > VCPU has been scheduled out since the last time the guest reset the bit. >> > The guest can use an xchg to test-and-clear it. The bit can be >> > accessed at any time, independent of the version field. >> >> If one vCPU is preempted, and guest check it several times before this >> vCPU is scheded in, then the first time we can get "vCPU is >> preempted", however, since the field is cleared, the second time we >> will get "vCPU is running". >> >> Do you mean we should call record_steal_time() in both kvm_sched_in() >> and kvm_sched_out() to record this field? Btw, if we should keep both >> vcpu->preempted and kvm_steal_time's "vCPU preempted" field present >> simultaneous? > > I suspect you want something like so; except this has holes in. > > We clear KVM_ST_PAD_PREEMPT before disabling preemption and we set it > after enabling it, this means that if we get preempted in between, the > vcpu is reported as running even though it very much is not. Paolo also point out this to me offline yesterday: "Please change pad[12] to "__u32 preempted; __u32 pad[11];" too, and remember to update Documentation/virtual/kvm/msr.txt!". Btw, do this in preemption notifier means that the vCPU is real preempted on host, however, depends on vmexit is different semantic I think. Regards, Wanpeng Li _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
