[libvirt] [PATCHv2 1/6] conf: add <irqchip mode> to <features>

[Ján Tomko]

On Mon, Apr 24, 2017 at 05:40:07PM -0400, John Ferlan wrote:
>
>
>On 04/20/2017 08:19 AM, Ján Tomko wrote:
>> Add a new <irqchip> element with a mode attribute.
>>
>> Possible values are off, split or on.
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1427005
>> ---
>>  docs/formatdomain.html.in                          | 10 +++++++
>>  docs/schemas/domaincommon.rng                      | 16 ++++++++++
>>  src/conf/domain_conf.c                             | 34 +++++++++++++++++++++-
>>  src/conf/domain_conf.h                             | 12 ++++++++
>>  .../qemuxml2argv-intel-iommu-irqchip.xml           | 29 ++++++++++++++++++
>>  .../qemuxml2xmlout-intel-iommu-irqchip.xml         |  1 +
>>  tests/qemuxml2xmltest.c                            |  1 +
>>  7 files changed, 102 insertions(+), 1 deletion(-)
>>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-intel-iommu-irqchip.xml
>>  create mode 120000 tests/qemuxml2xmloutdata/qemuxml2xmlout-intel-iommu-irqchip.xml
>>
>> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
>> index b1e38f0..abf089a 100644
>> --- a/docs/formatdomain.html.in
>> +++ b/docs/formatdomain.html.in
>> @@ -1643,6 +1643,7 @@
>>    </kvm>
>>    <pvspinlock state='on'/>
>>    <gic version='2'/>
>> +  <irqchip mode='split'/>
>>
>>  </features>
>>  ...</pre>
>> @@ -1804,6 +1805,15 @@
>>            for hypervisor to decide.
>>            <span class="since">Since 2.1.0</span>
>>        </dd>
>> +      <dt><code>irqchip</code></dt>
>> +      <dd>Tune the in-kernel irqchip. Possible values for the
>> +          <code>mode</code> attribute are:
>> +          <code>on</code>, <code>split</code> and <code>off</code>.
>> +          <code>split</code> is useful for using interrupt remapping
>> +          with the <a href="#elementsIommu">IOMMU device</a>.
>
>Something that isn't implemented until the subsequent patch, but I'm not
>against describing this feature a bit more here...
>

What would you say?

>I think most importantly what setting this feature will "do" would be
>useful.  How does someone know they need this?

It is needed if they want interrupt remapping for assigned devices.
They can find out from a guide like:
http://wiki.qemu.org/Features/VT-d#References
or the linked BZ, or from the error message QEMU reports when
they try to use interrupt remapping from libvirt without setting
this to "split".

> And secondarily what
>would it be required for? What does "on" really do?  IOW: What the
>difference between split and on.
>

IIUC options other than "split" aren't that useful.

Jan
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