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    SubjectRe: [PATCH RFC] kvm: deliver msix interrupts from irq handler
    On Thu, Jan 19, 2012 at 03:49:57PM +0200, Michael S. Tsirkin wrote:
    > > > + irq_rt = rcu_dereference(kvm->irq_routing);
    > > > + if (irq < irq_rt->nr_rt_entries)
    > > > + hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
    > > > + if (ei->type == KVM_IRQ_ROUTING_MSI)
    > > > + ret = kvm_set_msi(e, kvm, irq_source_id, level,
    > > > + host_irq);
    > > > + else
    > > > + ret = -EWOULDBLOCK;
    > > > + break;
    > > > + }
    > > > + rcu_read_unlock_bh();
    > > > + return ret;
    > > > +}
    > > > +
    > > Share implementation with kvm_set_irq().
    >
    > I considered this. There are several reasons not to do it:
    > - Amount of common code is very small
    Why? Just pass msi_only flag to kvm_set_irq() and skip an entry if flag is
    set and entry type is not msi.

    > - As it's separate, it's more obvious that it can't block (kvm_set_irq can block)
    > We can even tag kvm_set_irq with might_sleep.
    They can still be two separate function calling common one.

    > - This is way simpler and faster as we can do operations directly,
    > instead of copying the irq out, and as it's datapath
    > an optimization is I think justified.
    I really do not think the copy of one small data structure will be
    measurable. If it is (has to be proven) we can optimize that two
    in the common code.

    --
    Gleb.


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