Re: [Xen-devel] VT-d flush timeout

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.08.14 at 05:16, <yang.z.zhang@xxxxxxxxx> wrote:
> Jan Beulich wrote on 2014-08-19:
>>>>> "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> 08/19/14 3:34 AM >>>
>>> My only concern is that, for QI flush, the spin time relies on the
>>> length of the queue. I am not sure whether 1s is enough for worst
>>> case and I think we should remove the 1s in QI flush. And I think
>>> this also the same reason for Linux don't use timeout mechanism in QI flush.
>> 
>> First of all I think both Linux and Xen in the majority of cases waits
>> for completion of just individual queue entries. I.e. I'm not sure if
>> the practical worst case really is equal to the theoretical one. And
> 
> This is my guessing from Linux's implementation but may wrong.

Which is why we ask for you (the VT-d maintainer) to, as a first
step, supply a patch limiting the spinning time to a value smaller
than the current on, just enough to cover real requirements. The
second step then ought to be to rework the code to use
asynchronous operation (presumably including making use of the
respective IOMMU interrupt).

Jan


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