On 2023/11/03 18:35, Yuri Benditovich wrote:
On Thu, Nov 2, 2023 at 4:56 PM Akihiko Odaki <akihiko.od...@daynix.com <mailto:akihiko.od...@daynix.com>> wrote:On 2023/11/02 19:20, Yuri Benditovich wrote: > > > On Thu, Nov 2, 2023 at 11:33 AM Michael S. Tsirkin <m...@redhat.com <mailto:m...@redhat.com> > <mailto:m...@redhat.com <mailto:m...@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?
I was not clear, but I was talking about the case of vhost=off or peers other than tap (e.g., user). rss=on employs in-qemu RSS, which incurs overheads for such configurations.
