Messages in this thread | | | Date | Tue, 22 Dec 2009 21:25:20 +0200 | From | Avi Kivity <> | Subject | Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33 |
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On 12/22/2009 09:15 PM, 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. >
If you're not doing something pretty minor, you're better of waking up a thread (perhaps _sync if you want to keep on the same cpu). With the new user return notifier thingie, that's pretty cheap.
> 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. > >
It would be easier to add data logging support to ioeventfd, if it was needed that badly.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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