On Wed, Jan 12, 2022 at 05:30:47PM +0000, Sean Christopherson wrote: > On Wed, Jan 12, 2022, Peter Zijlstra wrote: > > On Wed, Jan 12, 2022 at 08:02:01PM +0800, Li RongQing wrote: > > > vcpu can schedule out when run halt instruction, and set itself > > > to INTERRUPTIBLE and switch to idle thread, vcpu should not be > > > set preempted for this condition > > > > Uhhmm, why not? Who says the vcpu will run the moment it becomes > > runnable again? Another task could be woken up meanwhile occupying the > > real cpu. > > Hrm, but when emulating HLT, e.g. for an idling vCPU, KVM will voluntarily schedule > out the vCPU and mark it as preempted from the guest's perspective. The vast majority, > probably all, usage of steal_time.preempted expects it to truly mean "preempted" as > opposed to "not running". No, the original use-case was locking and that really cares about running. If the vCPU isn't running, we must not busy-wait for it etc.. Similar to the scheduler use of it, if the vCPU isn't running, we should not consider it so. Getting the vCPU task scheduled back on the CPU can take a 'long' time. If you have pinned vCPU threads and no overcommit, we have other knobs to indicate this I tihnk.
