Messages in this thread | | | Date | Wed, 17 Dec 2014 18:11:00 +0100 | From | Paolo Bonzini <> | Subject | Re: [v3 23/26] KVM: Update Posted-Interrupts Descriptor when vCPU is preempted |
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On 12/12/2014 16:14, Feng Wu wrote: > + if (irq_remapping_cap(IRQ_POSTING_CAP)) { > + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); > + struct pi_desc old, new; > + unsigned int dest; > + > + memset(&old, 0, sizeof(old)); > + memset(&new, 0, sizeof(new));
This is quite expensive. Just use an u64 for old_control and new_control, instead of a full struct.
> > + pi_clear_sn(&new);
This can be simply new.sn = 0. It does not need atomic operations.
Same in patch 24 (if needed at all there---see the reply there).
> > + if (irq_remapping_cap(IRQ_POSTING_CAP)) { > + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); > + struct pi_desc old, new; > + > + memset(&old, 0, sizeof(old)); > + memset(&new, 0, sizeof(new)); > +
Here you do not need old/new at all because...
> + if (vcpu->preempted) { > + do { > + old.control = new.control = pi_desc->control; > + pi_set_sn(&new); > + } while (cmpxchg(&pi_desc->control, old.control, > + new.control) != old.control);
this can do pi_set_sn directly on pi_desc, without the cmpxchg.
Paolo
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