On Thu, Jan 19, 2012 at 05:02:17PM +0200, Gleb Natapov wrote:
> 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.
No, the common code is the surrounding foreach loop,
the internal if branch is different.
> > - 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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