lkml.org 
[lkml]   [2019]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH RESEND] KVM: Boosting vCPUs that are delivering interrupts
    From
    Date
    On 18/07/19 11:29, Wanpeng Li wrote:
    > On Thu, 18 Jul 2019 at 17:07, Paolo Bonzini <pbonzini@redhat.com> wrote:
    >>
    >> On 18/07/19 10:43, Wanpeng Li wrote:
    >>>>> Isnt that done by the sched_in handler?
    >>>>
    >>>> I am a bit confused because, if it is done by the sched_in later, I
    >>>> don't understand why the sched_out handler hasn't set vcpu->preempted
    >>>> already.
    >>>>
    >>>> The s390 commit message is not very clear, but it talks about "a former
    >>>> sleeping cpu" that "gave up the cpu voluntarily". Does "voluntarily"
    >>>> that mean it is in kvm_vcpu_block? But then at least for x86 it would
    >>>
    >>> see the prepare_to_swait_exlusive() in kvm_vcpu_block(), the task will
    >>> be set in TASK_INTERRUPTIBLE state, kvm_sched_out will set
    >>> vcpu->preempted to true iff current->state == TASK_RUNNING.
    >>
    >> Ok, I was totally blind to that "if" around vcpu->preempted = true, it's
    >> obvious now.
    >>
    >> I think we need two flags then, for example vcpu->preempted and vcpu->ready:
    >>
    >> - kvm_sched_out sets both of them to true iff current->state == TASK_RUNNING
    >>
    >> - kvm_vcpu_kick sets vcpu->ready to true
    >>
    >> - kvm_sched_in clears both of them

    ... and also kvm_vcpu_on_spin should check vcpu->ready. vcpu->preempted
    remains only for use by vmx_vcpu_pi_put.

    Later we could think of removing vcpu->preempted. For example,
    kvm_arch_sched_out and kvm_x86_ops->sched_out could get the code
    currently in vmx_vcpu_pi_put (testing curent->state == TASK_RUNNING
    instead of vcpu->preempted). But for now there's no need and I'm not
    sure it's an improvement at all.

    Paolo

    >> This way, vmx_vcpu_pi_load can keep looking at preempted only (it
    >> handles voluntary preemption in pi_pre_block/pi_post_block).

    \
     
     \ /
      Last update: 2019-07-18 11:40    [W:4.324 / U:0.224 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site