Re: [Qemu-devel] [RFC][PATCH 28/45] qemu-kvm: msix: Drop tracking of used vectors

[Jan Kiszka]

On 2011-10-18 17:22, Jan Kiszka wrote:
> What KVM has to do is just mapping an arbitrary MSI message
> (theoretically 64+32 bits, in practice it's much of course much less) to

( There are 24 distinguishing bits in an MSI message on x86, but that's
only a current interpretation of one specific arch. )

> a single GSI and vice versa. As there are less GSIs than possible MSI
> messages, we could run out of them when creating routes, statically or
> lazily.
> 
> What would probably help us long-term out of your concerns regarding
> lazy routing is to bypass that redundant GSI translation for dynamic
> messages, i.e. those that are not associated with an irqfd number or an
> assigned device irq. Something like a KVM_DELIVER_MSI IOCTL that accepts
> address and data directly.

This would be a trivial extension in fact. Given its beneficial impact
on our GSI limitation issue, I think I will hack up something like that.

And maybe this makes a transparent cache more reasonable. Then only old
host kernels would force us to do searches for already cached messages.

Jan

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