Re: [libvirt] [PATCH v2] qemu: Add option to enable/disable IOEventFD feature

[Daniel Veillard <veillard redhat com>]

On Tue, May 17, 2011 at 03:56:11PM +0100, Daniel P. Berrange wrote:
> On Tue, May 17, 2011 at 04:49:17PM +0200, Michal Privoznik wrote:
> > This feature allows QEMU to achieve higher throughput, but is available
> > only in recent versions. It is accessible via ioeventfd attribute
> > with accepting values 'on', 'off'. Only experienced users needs to set
> > this, because QEMU defaults to 'on', meaning higher performance.
> > Translates into virtio-{blk|net}-pci.ioeventfd option.
[...]
> > +          <li>
> > +           The optional <code>ioeventfd</code> attribute enables or disables
> > +           IOEventFD feature for virtqueue notify. The value can be either
> > +           'on' or 'off'.
> > +            <span class="since">Since 0.9.2 (QEMU and KVM only)</span>
> 
> This is a qemu specific attribute name & description. IMHO we shouldn't
> be exposing that directly. Who even knows what effect it actually has
> on the guests...

  Agreed, what is the semantic of this flag, beside allowing to switch
something in qemu ?

Daniel

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