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Subject: Re: [virtio-comment] Re: [PATCH] virtio-net: define feature of per-packet RSS hash delivery
On Thu, Dec 12, 2019 at 05:48:22AM +0200, Yuri Benditovich wrote: > On Wed, Dec 11, 2019 at 8:20 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > On Wed, Dec 11, 2019 at 07:41:59PM +0200, Yuri Benditovich wrote: > > > On Wed, Dec 11, 2019 at 6:35 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > On Wed, Dec 04, 2019 at 12:20:01AM -0500, Yuri Benditovich wrote: > > > > > > > > > > > > > > > âââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ > > > > > > > > > > From: "Michael S. Tsirkin" <mst@redhat.com> > > > > > To: "Yuri Benditovich" <yuri.benditovich@daynix.com> > > > > > Cc: virtio-comment@lists.oasis-open.org > > > > > Sent: Tuesday, December 3, 2019 10:25:30 PM > > > > > Subject: [virtio-comment] Re: [PATCH] virtio-net: define feature of > > > > > per-packet RSS hash delivery > > > > > > > > > > On Tue, Dec 03, 2019 at 08:32:12PM +0200, Yuri Benditovich wrote: > > > > > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/66 > > > > > > Conditional extending of virtio header structure to deliver > > > > > > packet's hash and hash type used for calculation. > > > > > > > > > > > > Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com> > > > > > > > > > > Functionally this looks mostly good. But we need to change the > > > > > way it's documented slightly. > > > > > > > > > > Probably, because the RSS patch is not merged yet. > > > > > > > > > > > > > > > > --- > > > > > > content.tex | 24 ++++++++++++++++++++++++ > > > > > > 1 file changed, 24 insertions(+) > > > > > > > > > > > > diff --git a/content.tex b/content.tex > > > > > > index 01be7df..44975e4 100644 > > > > > > --- a/content.tex > > > > > > +++ b/content.tex > > > > > > @@ -2811,6 +2811,9 @@ \subsection{Feature bits}\label{sec:Device Types / > > > > > Network Device / Feature bits > > > > > > \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control > > > > > > channel. > > > > > > > > > > > > +\item[VIRTIO_NET_F_HASH_REPORT(58)] Device can report per-packet hash > > > > > value > > > > > > + and a type of calculated hash > > > > > > + > > > > > > \item[VIRTIO_NET_F_RSS(60)] Device supports RSS (receive-side scaling) > > > > > > with Toeplitz hash calculation and configurable hash parameters for > > > > > receive steering > > > > > > > > > > > > @@ -2844,6 +2847,8 @@ \subsubsection{Feature bit requirements}\label > > > > > {sec:Device Types / Network Device > > > > > > \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ. > > > > > > \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or > > > > > VIRTIO_NET_F_HOST_TSO6. > > > > > > \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ. > > > > > > +\item[VIRTIO_NET_F_HASH_REPORT] Requires VIRTIO_NET_F_RSS. > > > > > > + > > > > > > \end{description} > > > > > > > > > > > > \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / > > > > > Network Device / Feature bits / Legacy Interface: Feature bits} > > > > > > @@ -3071,6 +3076,8 @@ \subsection{Device Operation}\label{sec:Device > > > > > Types / Network Device / Device O > > > > > > le16 csum_start; > > > > > > le16 csum_offset; > > > > > > le16 num_buffers; > > > > > > + le32 hash_value; (Only if VIRTIO_NET_F_HASH_REPORT negotiated) > > > > > > + le16 hash_type; (Only if VIRTIO_NET_F_HASH_REPORT negotiated) > > > > > > }; > > > > > > \end{lstlisting} > > > > > > > > > > > > @@ -3330,6 +3337,15 @@ \subsubsection{Processing of Incoming Packets}\ > > > > > label{sec:Device Types / Network > > > > > > set: if so, device has validated the packet checksum. > > > > > > In case of multiple encapsulated protocols, one level of checksums > > > > > > has been validated. > > > > > > +\item If VIRTIO_NET_F_HASH_REPORT was negotiated and a device has > > > > > calculated > > > > > > + a hash for the packet, \field{hash_value} contains calculated hash > > > > > value and > > > > > > + \field{hash_type} contains exact hash type. > > > > > > + > > > > > > + If the hash was not calculated, \field{hash_type} contains zero. > > > > > > + > > > > > > + For defined hash types and their meaning, see \ref{sec:Device Types / > > > > > Network Device / Device configuration layout / RSS}. > > > > > > + > > > > > > + For the procedure of hash calculation, see \ref{sec:Device Types / > > > > > Network Device / Device Operation / Control Virtqueue / Receive-side > > > > > scaling (RSS) / RSS hash types}. > > > > > > \end{enumerate} > > > > > > > > > > > > Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP and ECN > > > > > > @@ -3909,6 +3925,14 @@ \subsubsection{Control Virtqueue}\label{sec:Device > > > > > Types / Network Device / Devi > > > > > > \item Else skip IPv6 extension headers and calculate the hash as defined > > > > > above for IPv6 packet without extension headers > > > > > > \end{itemize} > > > > > > > > > > > > +If VIRTIO_NET_F_HASH_REPORT was negotiated, the device reports > > > > > calculated hash information in fields of virtio_net_hdr as follows: > > > > > > + > > > > > > +Exact hash type is populated in \field{hash_type} > > > > > > + > > > > > > +Hash value is populated in \field{hash_value} > > > > > > + > > > > > > +If, due to any reason, the device did not calculate the hash, it sets \ > > > > > field{hash_type} to zero. > > > > > > + > > > > > > \drivernormative{\subparagraph}{Setting RSS parameters}{Device Types / > > > > > Network Device / Device Operation / Control Virtqueue / Receive-side > > > > > scaling (RSS) } > > > > > > > > > > > > A driver MUST NOT send the VIRTIO_NET_CTRL_MQ_RSS_CONFIG command if the > > > > > feature VIRTIO_NET_F_RSS has not been negotiated. > > > > > > > > > > > > > > > This is understandably a minimal change, but imho messes things up: > > > > > hash calculation is no longer part of RSS so really should be moved > > > > > from out of there. > > > > > > > > > > Please advise why "hash calculation is no longer part of RSS". > > > > > > > > I might be misunderstanding things. It looks like with this > > > > one can enable hash even with a single RX queue. > > > > No? > > > > > > Not exactly. > > > Hash calculation (even with single queue, which is possible corner > > > case) requires a key to be configured with > > > VIRTIO_NET_CTRL_MQ_RSS_CONFIG command. > > > So, if the device with one queue is capable to deliver the hash it > > > indicates VIRTIO_NET_F_RSS and VIRTIO_NET_F_HASH_REPORT. > > > I will add this. > > > And probably the device should deny VIRTIO_NET_F_HASH_REPORT without > > > VIRTIO_NET_F_RSS. > > > > Oh I see. Interesting. Do we want to tie the two features like this though? > > I wonder why? > > If yes we can certainly make VIRTIO_NET_F_HASH_REPORT depend on RSS ... > > If not there could be a variant of VIRTIO_NET_CTRL_MQ_RSS_CONFIG > > without RSS tables that's allowed without RSS. > > > IMO: > VIRTIO_NET_CTRL_MQ_RSS_CONFIG defines 2 things mandatory for hash calculation: > 1) a key > 2) set of allowed hashes - this may change the calculation even on the > same packet > So IMO, VIRTIO_NET_F_HASH_REPORT depends on VIRTIO_NET_F_RSS. > > If you have a use case that make sense of having only > VIRTIO_NET_F_HASH_REPORT, please describe it. Hashes are handy for forwarding packets. So bridging within guest, where we prefer auto-mq to avoid manually worrying about queue assignment, and with a hardware virtio device that can calculate the hashes for free for us. > > > > > > > > > > > > > > > > > > > So we'd have a chapter for hash calculation, defining hash types > > > > > etc. > > > > > > > > > > A chapter for hash calculation is in previous patch > > > > > https://lists.oasis-open.org/archives/virtio-comment/201911/msg00014.html > > > > > > > > > > > > > Can't see it there. Do you mean > > > > +\subparagraph{RSS hash types}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS hash types} > > > > ? > > > > Sure, what I am saying it needs to be moved from out of RSS then. > > > > > > > > > > I do not see how hash calculation can be moved out of RSS, it requires > > > the configuration that comes with VIRTIO_NET_CTRL_MQ_RSS_CONFIG. > > > > Allow VIRTIO_NET_CTRL_MQ_RSS_CONFIG with no RSS parameters > > when RSS is off? > > > > When in VIRTIO_NET_CTRL_MQ_RSS_CONFIG the max_tx_vq=1: > * if VIRTIO_NET_F_HASH_REPORT is not negotiated the rest of parameters > can be ignored as there is nothing to do with them. > * if VIRTIO_NET_F_HASH_REPORT is negotiated, a key and hash_types are used. > So, for consistency, I would not invent new format of > VIRTIO_NET_CTRL_MQ_RSS_CONFIG Right. So we could rename e.g. VIRTIO_NET_CTRL_MQ_RSS_CONFIG to something like VIRTIO_NET_CTRL_MQ_RSS_HASH_CONFIG and allow that without RSS. > > > > > > > > > > Then both RSS and the new chapter refer to that. > > > > > > > > > > Also, I am guessing supported hash types should be valid > > > > > in config space with the new feature - isn't that right? > > > > > > > > > > Yes, of course. > > > > > > > > So we need to say this in the spec I think. > > > > > > OK, I will add this. > > > To avoid misunderstandings I think it is better to wait until the RSS > > > patch (mentioned above) is merged. > > > When approx. we can expect that? > > > > Could of days, my laptop was in repair, so there's a backlog of > > things to merge. > > > > > > > > > > > But this is not related to hash delivery. > > > > > Packet hash is calculated according to allowed hash types. > > > > > If hash delivery is negotiated, the device reports the calculated hash type > > > > > which is, naturally, one of valid ones. > > > > > > > > > > > > > > > > > > > > > -- > > > > > > 2.17.2 > > > > > > > > > > > > > > > This publicly archived list offers a means to provide input to the > > > > > OASIS Virtual I/O Device (VIRTIO) TC. > > > > > > > > > > In order to verify user consent to the Feedback License terms and > > > > > to minimize spam in the list archive, subscription is required > > > > > before posting. > > > > > > > > > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > > > > > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > > > > > List help: virtio-comment-help@lists.oasis-open.org > > > > > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > > > > > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > > > > > List Guidelines: https://www.oasis-open.org/policies-guidelines/ > > > > > mailing-lists > > > > > Committee: https://www.oasis-open.org/committees/virtio/ > > > > > Join OASIS: https://www.oasis-open.org/join/ > > > > > > > > > > > > > > > > > > > > > > > > > This publicly archived list offers a means to provide input to the > > OASIS Virtual I/O Device (VIRTIO) TC. > > > > In order to verify user consent to the Feedback License terms and > > to minimize spam in the list archive, subscription is required > > before posting. > > > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > > List help: virtio-comment-help@lists.oasis-open.org > > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > > Committee: https://www.oasis-open.org/committees/virtio/ > > Join OASIS: https://www.oasis-open.org/join/ > >
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