On Thu, Mar 02 2006, Andi Kleen wrote:
> On Thursday 02 March 2006 15:14, Jens Axboe wrote:
>
> [...]
>
> Ok great we agree on everything then.
Seems so :)
> > > >
> > > > I would not want to call wake_up() unless I have to. Would a
> > > >
> > > > smp_mb();
> > > > if (waitqueue_active(&iommu_wq))
> > > > ...
> > > >
> > > > not be sufficient?
> > >
> > > Probably, but one would need to be careful to not miss events this way.
> >
> > Definitely, as far as I can see the above should be enough...
>
> Ok - you just need to give me a wait queue then and I would be happy
> to add the wakeups to the low level code
>
> (or you can just do it yourself if you prefer, shouldn't be very
> difficult ... - just needs to be done for both swiotlb and GART iommu.
> The other architectures can follow then. At the beginning using an
> ARCH_HAS_* ifdef might be a good idea for easier transition for
> everybody)
I'd prefer adding that wait queue in the iommu code, it's where it
belongs. Didn't we agree on just a global waitqueue? The the interface
for block/net/whatever-consume would just be something like:
iommu_wait();
which would return when we have enough space, hopefully. A subsystem
specific waitqueue would have the handy side of supplying a callback on
the wake up, which would be a nicer design. But isn't the enough
wait_for_resources() call sufficient for this?
--
Jens Axboe
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