2016-07-07 18:12 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: > 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. In addition, I see xen's vcpu_runstate_info::state is updated during schedule, so I think I can do this similarly through kvm preemption notifier. IIUC, xen hypervisor has VCPUOP_get_runstate_info hypercall implemention, so the desired interface can be implemented if they add hypercall callsite in domU. I can add hypercall to kvm similarly. Paolo, thoughts? Regards, Wanpeng Li _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
