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Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq

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On 17/02/2016 20:14, Radim Krčmář wrote:
> -	value = atomic_dec_return(&ps->pending);
> -	if (value < 0)
> -		/* spurious acks can be generated if, for example, the
> -		 * PIC is being reset.  Handle it gracefully here
> -		 */
> -		atomic_inc(&ps->pending);
> -	else if (value > 0 && ps->reinject)
> -		/* in this case, we had multiple outstanding pit interrupts
> -		 * that we needed to inject.  Reinject
> -		 */
> +	if (atomic_dec_if_positive(&ps->pending) > 0 && ps->reinject)
>  		queue_kthread_work(&ps->pit->worker, &ps->pit->expired);

Here it would have made sense to do already

	if (!ps->reinject) {
		WARN_ON_ONCE(ps->pending || !ps->irq_ack);
		return;
	}
	spin_lock(...)
	if (atomic_dec_if_positive(&ps->pending) > 0)
		queue_kthread_work(...);
	ps->irq_ack = 1;
	spin_unlock(...)
	
because ps->pending is only ever nonzero, and irq_ack is only ever zero,
if ps->reinject.  Not a big deal since the ack notifier is going to
disappear altogether for the discard policy, but the nice thing is that
it lets you remove the ack notifier earlier and disentangle a bit more
discard mode.

So if you want for v3 you can reorder the patches like this:

- patch 1, same

- patch 2, what is outlined above

- patch 3, remove ack notifier for discard

- patch 4..14 the rest

Paolo

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[PATCH v2 00/14] KVM: x86: change PIT discard policy and untangle related code Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 17:00 +0100
      Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 17:00 +0100
  [PATCH v2 14/14] KVM: x86: move PIT timer function initialization Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 05/14] KVM: x86: tone down WARN_ON pit.state_lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 06/14] KVM: x86: pass struct kvm_pit instead of kvm in PIT Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 09/14] KVM: x86: refactor kvm_create_pit Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 04/14] KVM: x86: use atomic_t instead of pit.inject_lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 13/14] KVM: x86: don't assume layout of kvm_kpit_state Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 17:20 +0100
      Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-18 18:00 +0100
        Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 18:40 +0100
          Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:00 +0100
            Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 15:50 +0100
    Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:50 +0100
  [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
    Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 16:10 +0100
        Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 16:10 +0100
          Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 16:10 +0100
  [PATCH v2 10/14] KVM: x86: refactor kvm_free_pit Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 11/14] KVM: x86: remove pit and kvm from kvm_kpit_state Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state  lock Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state  lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 15:50 +0100
  [PATCH v2 03/14] KVM: x86: add kvm_pit_reset_reinject Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:30 +0100
  Re: [PATCH v2 00/14] KVM: x86: change PIT discard policy and untangle  related code Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:20 +0100

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