Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

Davide Libenzi
2009-12-22T19:39:55Z

On Tue, 22 Dec 2009, Gregory Haskins wrote:

> On 12/22/09 1:53 PM, Avi Kivity wrote:
> > I asked why the irqfd/ioeventfd mechanisms are insufficient, and you did not reply.
> >
>
> BTW: the ioeventfd issue just fell through the cracks, so sorry about
> that. Note that I have no specific issue with irqfd ever since the
> lockless IRQ injection code was added.
>
> ioeventfd turned out to be suboptimal for me in the fast path for two
> reasons:
>
> 1) the underlying eventfd is called in atomic context. I had posted
> patches to Davide to address that limitation, but I believe he rejected
> them on the grounds that they are only relevant to KVM.

I thought we addressed this already, in the few hundreds of email we
exchanged back then :)

> 2) it cannot retain the data field passed in the PIO. I wanted to have
> one vector that could tell me what value was written, and this cannot be
> expressed in ioeventfd.

Like might have hinted in his reply, couldn't you add data support to the
ioeventfd bits in KVM, instead of leaking them into mainline eventfd?

- Davide