On 2023/11/02 19:20, Yuri Benditovich wrote:
>
>
> On Thu, Nov 2, 2023 at 11:33 AM Michael S. Tsirkin <mst@redhat.com
> <mailto:mst@redhat.com>> wrote:
>
> On Thu, Nov 02, 2023 at 11:09:27AM +0200, Yuri Benditovich wrote:
> > Probably we mix two different patches in this discussion.
> > Focusing on the patch in the e-mail header:
> >
> > IMO it is not acceptable to fail QEMU run for one feature that we
> can't make
> > active when we silently drop all other features in such a case.
>
> If the feature is off by default then it seems more reasonable
> and silent masking can be seen as a bug.
> Most virtio features are on by default this is why it's
> reasonable to mask them.
>
>
> If we are talking about RSS: setting it initially off is the development
> time decision.
> When it will be completely stable there is no reason to keep it off by
> default, so this is more a question of time and of a readiness of libvirt.
It is not ok to make "on" the default; that will enable RSS even when
eBPF steering support is not present and can result in performance
degradation.
Exactly as it is today - with vhost=on the host does not suggest RSS without eBPF.
I do not understand what you call "performance degradation", can you describe the scenario?
We will need OnOffAuto instead of a simple boolean value if we are going
to enable RSS when eBPF steering support is available; "auto" will be
the default and will enable RSS if and only if eBPF steering support is
available. "on" will not be default so it's better to validate if RSS is
available when the user explicitly specified "on" for the "rss" property.