[vfio-users] posted interrupts

[Joshua Lee]

I was told that E5 16xxV4 does have posted interrupts as an option.
However, apparently it affects compute performance more than other things
and doesn't help much for graphics speed in PCIe passthrough, according to
a fellow I talked to on Freenode. So I think I'll stick to an i7, at least
until Broadwell-EP with the same or more cores and optimized frequency are
as cheap as Sandy Bridge or Westmere Xeons... Thanks for your offer of
help. (You may still want to look into posted interrupts kernel options for
your Broadwell-EP processor for your own use.)


On Thu, Apr 6, 2017 at 5:35 PM, Joshua Lee <joshua613 at gmail.com> wrote:

> I saw it online somewhere, but forgot the kernel parameter... I'll try to
> find it, and anything else you might need to know.
>
> On Thu, Apr 6, 2017 at 5:00 PM, P. Pronk <vfio at pronk.nl> wrote:
>
>>
>> not sure which kernel parameter or libvirt option that would be either
>> unfortunately.
>>
>> If you or someone else can point to some clear directions I am still
>> happy to help.
>>
>> On 06/04/17 20:06, Joshua Lee wrote:
>>
>> If you get that running, run FIrestrike both "before and after" using
>> posted interrupts for me... and show what scores you get, maybe some other
>> benchmark like one of the ones from Unigine if you have the time.
>>
>> On Thu, Apr 6, 2017 at 1:00 PM, Joshua Lee <joshua613 at gmail.com> wrote:
>>
>>> I'm not sure, I know there's a kernel command line argument that
>>> activates support for it, then there might be something also within your
>>> libvirt XML and QEMU command-line?
>>>
>>> On Thu, Apr 6, 2017 at 8:00 AM, P. Pronk <vfio at pronk.nl> wrote:
>>>
>>>>
>>>> With regards to your first question, I am using an E5-1620v4 with X99
>>>> chipset but I am not sure how I can check for you if the 16xx supports
>>>> this. Let me know if you would like me to check something specifically.
>>>>
>>>> Kind regards, Pim
>>>>
>>>> On 06/04/17 13:18, Joshua Lee wrote:
>>>>
>>>> I'm not clear if posted interrupts, a feature of Broadwell-EP, is
>>>> available on both E5 1xxx V4 and E5 2xxx V4, or just E5 2xxx V4? Intel's
>>>> marketing literature seems to stress the latter family of processors as
>>>> having it, but reviews on sources such as Anandtech do not mention anything
>>>> but Broadwell-EP E5 Xeons having it in general.
>>>>
>>>> Also, a second question, what amount of performance increase in GPU
>>>> performance could one expect for a KVM/QEMU virtual machine with PCIE VGA
>>>> passthrough using the posted interrupt feature of Broadwell-EP Xeons, using
>>>> say a 1620 V4, 1630 V4, or 1650 V4, assuming those have the feature (if
>>>> not, insert a frequency-optimized E5 2xxx instead) versus say a i7-5820k?
>>>>
>>>>
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>>>
>
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