Re: [Xen-devel] [PATCH v10 1/3] vt-d: add a timeout parameter for Queued Invalidation

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> "Xu, Quan" <quan.xu@xxxxxxxxx> 05/19/16 3:35 AM >>>
>On May 19, 2016 8:33 AM, Tian, Kevin <kevin.tian@xxxxxxxxx> wrote:
>> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> > Sent: Wednesday, May 18, 2016 11:05 PM
>> > >>> On 18.05.16 at 14:53, <quan.xu@xxxxxxxxx> wrote:
>> > The patch can imo remain as is only if the new default timeout is
>> > large enough for all possible cases (including those users who are
>> > adventurous enough to turn on ATS).
>
>I only have an ATS device (MYRICOM Inc. Myri-10G Dual-Protocol NIC). 1 ms is 
>large enough for invalidation so far.
>Any suggestion for this new default timeout?

Unless you have theoretical proof that a lower than the current value would
suffice (as you do for the IOMMU side flushes), I think the default needs to
remain the same as it is right now (which iirc is already _much_ lower than
the real theoretical one).

>> A single default value for both IOMMU-side and device-side is anyway not
>> optimal. What about introducing a new knob e.g. vtd_qi_device_timeout
>> specifically for device-side flush while using vtd_qi_timeout for other 
>> places? If
>> device-side timeout is not specified, it is then default to vtd_qi_timeout.

There should imo be a single command line option, allowing for two values to be
passed (e.g. comma-separated).

Jan


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