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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.08.14 at 09:49, <yang.z.zhang@xxxxxxxxx> wrote:
> 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.

Because it reduces the impact the currently large value would have
in misbehaving cases? Don clearly indicated to me that it shouldn't
be a big deal to reduce the current timeout, so I really don't see what
all this argument is about.

Jan


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