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

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 @@ > &lt;/kvm&gt; > &lt;pvspinlock state='on'/&gt; > &lt;gic version='2'/&gt; > + &lt;irqchip mode='split'/&gt; > > &lt;/features&gt; > ...</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...

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

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