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

Jan Beulich wrote on 2014-08-22:
>>>> 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

This doesn't answer my question. I still don't see why a smaller value helps.

> then ought to be to rework the code to use asynchronous operation
> (presumably including making use of the respective IOMMU interrupt).
> Jan

Best regards,

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