Re: [Xen-devel] [PATCH] VT-d: Chop down the DMAR_OPERATION_TIMEOUT to a low number of milliseconds.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.16 at 08:16, <quan.xu@xxxxxxxxx> wrote:
> We confirmed with VT-d hardware team that 1ms is large enough for IOMMU
> internal flush. So We can change the DMAR_OPERATION_TIMEOUT from 1000 ms
> to 1 ms.

First of all the description mentions just one of the two uses of
this constant. And then I'm hesitant to commit this as long as the
panic()-s are still there when that timeout expires - reducing the
timeout (the more this significantly) will raise the (theoretical)
chance of actually invoking one of them. Hence the proper order
in which I would like to see things happen is for this to be reduced
only after having
- eliminated the panic()-s
- decoupled the device IOTLB invalidation from this path (after
  all right now flush_iotlb_qi() uses invalidate_sync() for both,
  and hence the shortened timeout now pretty certainly is too
  short for the device IOTLB case)

Temporarily it may be sufficient to just eliminate the panic()-s,
provided the timeout value would then be made dependent on
ats_enabled.

Jan


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