Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

Gregory Haskins
2009-12-22T19:15:38Z

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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.

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.

Based on this, it was a better decision to add a ioevent interface to
xinterface. It neatly solves both problems.

Kind Regards,
-Greg

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