From: Akihiko Odaki <akihiko.odaki@daynix.com>
To: Yuri Benditovich <yuri.benditovich@daynix.com>,
Jason Wang <jasowang@redhat.com>
Cc: qemu-devel@nongnu.org, Andrew Melnychenko <andrew@daynix.com>,
"Michael S . Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v6 11/21] virtio-net: Return an error when vhost cannot enable RSS
Date: Mon, 30 Oct 2023 22:14:55 +0900 [thread overview]
Message-ID: <8880b6f9-f556-46f7-a191-eeec0fe208b0@daynix.com> (raw)
In-Reply-To: <CAOEp5Oern10jW8Pi-_mceU_ZJVD=a1f3tW8rB2O4efLX45-nvw@mail.gmail.com>
On 2023/10/30 21:51, Yuri Benditovich wrote:
>
>
> On Mon, Oct 30, 2023 at 2:21 PM Akihiko Odaki <akihiko.odaki@daynix.com
> <mailto:akihiko.odaki@daynix.com>> wrote:
>
> On 2023/10/30 21:14, Yuri Benditovich wrote:
> >
> >
> > On Mon, Oct 30, 2023 at 7:14 AM Akihiko Odaki
> <akihiko.odaki@daynix.com <mailto:akihiko.odaki@daynix.com>
> > <mailto:akihiko.odaki@daynix.com
> <mailto:akihiko.odaki@daynix.com>>> wrote:
> >
> > vhost requires eBPF for RSS. When eBPF is not available,
> virtio-net
> > implicitly disables RSS even if the user explicitly requests
> it. Return
> > an error instead of implicitly disabling RSS if RSS is
> requested but not
> > available.
> >
> >
> > I think that suggesting RSS feature when in fact it is not
> available is
> > not a good idea, this rather desinforms the guest.
> > Existing behavior (IMHO) makes more sense.
> > We can extend this discussion if needed, of course.
>
> This change is not to advertise RSS when it's not available; it instead
> reports an error to the user.
>
> For example, think of the following command line:
> qemu-system-x86_64 -device virtio-net,rss=on,netdev=n -netdev user,id=n
>
> Before this change, it gives no error and the user will not know RSS is
> not available. With this change it now gives an error as follows:
> qemu-system-x86_64: -device virtio-net,rss=on,netdev=n: Can't load
> eBPF RSS
>
>
> Does this mean failure to run QEMU if the RSS required in the command
> line and EBPF can't be loaded?
> (for example if we run the system with kernel < 5.8)?
> I'm not sure this is user-friendly behavior...
This patch is wrong that it assumes software RSS is not enabled at all;
I missed the vhost check before clearing VIRTIO_NET_F_RSS in
virtio_net_get_features().
That said, I indeed intend to make it return a hard error for the case
that RSS is requested for vhost but eBPF can't be loaded.
I believe the current behavior of implicitly disabling a feature
explicitly requested by the user is not good, but we can still emit a
warning instead of an error.
It's better to follow a convention common in QEMU but I see no
documentation regarding this kind of situation. I know virtio-gpu gives
an error in such a case but it's just one example.
I'd also like to ask Jason if we should have a warning or error. Perhaps
we may better consult QOM maintainers too.
next prev parent reply other threads:[~2023-10-30 13:16 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-30 5:12 [PATCH v6 00/21] virtio-net RSS/hash report fixes and improvements Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 01/21] tap: Remove tap_probe_vnet_hdr_len() Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 02/21] tap: Remove qemu_using_vnet_hdr() Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 03/21] net: Move virtio-net header length assertion Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 04/21] net: Remove receive_raw() Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 05/21] tap: Remove tap_receive() Akihiko Odaki
2023-10-30 18:52 ` Zhang, Chen
2023-10-31 4:57 ` Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 06/21] net: Remove flag propagation Akihiko Odaki
2023-11-10 7:35 ` Pavel Dovgalyuk
2023-11-11 14:27 ` Akihiko Odaki
2023-11-13 8:14 ` Pavel Dovgalyuk
2023-10-30 5:12 ` [PATCH v6 07/21] tap: Shrink zeroed virtio-net header Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 08/21] virtio-net: Copy header only when necessary Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 09/21] virtio-net: Disable RSS on reset Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 10/21] virtio-net: Unify the logic to update NIC state for RSS Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 11/21] virtio-net: Return an error when vhost cannot enable RSS Akihiko Odaki
2023-10-30 12:14 ` Yuri Benditovich
2023-10-30 12:21 ` Akihiko Odaki
2023-10-30 12:51 ` Yuri Benditovich
2023-10-30 13:14 ` Akihiko Odaki [this message]
2023-11-01 4:19 ` Jason Wang
2023-11-01 4:50 ` Akihiko Odaki
2023-11-01 6:38 ` Michael S. Tsirkin
2023-11-01 8:35 ` Akihiko Odaki
2023-11-01 9:09 ` Michael S. Tsirkin
2023-11-01 9:15 ` Akihiko Odaki
2023-11-02 9:09 ` Yuri Benditovich
2023-11-02 9:33 ` Michael S. Tsirkin
2023-11-02 10:20 ` Yuri Benditovich
2023-11-02 11:26 ` Michael S. Tsirkin
2023-11-02 12:00 ` Yuri Benditovich
2023-11-02 13:18 ` Michael S. Tsirkin
2023-11-02 14:56 ` Akihiko Odaki
2023-11-03 9:35 ` Yuri Benditovich
2023-11-03 9:55 ` Akihiko Odaki
2023-11-03 13:14 ` Yuri Benditovich
2023-11-11 15:28 ` Akihiko Odaki
2023-11-13 11:44 ` Yuri Benditovich
2023-11-13 12:44 ` Akihiko Odaki
2023-11-13 17:26 ` Yuri Benditovich
2023-11-14 7:03 ` Akihiko Odaki
2023-11-14 22:09 ` Yuri Benditovich
2023-11-15 6:09 ` Akihiko Odaki
2023-11-16 5:14 ` Jason Wang
2023-10-30 5:12 ` [PATCH v6 12/21] virtio-net: Enable software RSS Akihiko Odaki
2023-10-30 12:42 ` Yuri Benditovich
2023-10-30 5:12 ` [PATCH v6 13/21] virtio-net: Always set populate_hash Akihiko Odaki
2023-10-30 19:02 ` Zhang, Chen
2023-10-31 4:47 ` Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 14/21] virtio-net: Do not write hashes to peer buffer Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 15/21] virtio-net: Do not clear VIRTIO_NET_F_HASH_REPORT Akihiko Odaki
2023-11-03 13:26 ` Yuri Benditovich
2023-10-30 5:12 ` [PATCH v6 16/21] ebpf: Fix RSS error handling Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 17/21] ebpf: Use standard section name Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 18/21] ebpf: Simplify error handling Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 19/21] ebpf: Return 0 when configuration fails Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 20/21] ebpf: Refactor tun_rss_steering_prog() Akihiko Odaki
2023-10-30 5:12 ` [PATCH v6 21/21] ebpf: Add a separate target for skeleton Akihiko Odaki
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