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Subject: Re: [virtio-comment] Re: [PATCH] virtio-net: define feature of per-packet RSS hash delivery
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.
>
> >
> >
> > 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.
> >
> > 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?
>
> > 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
> >
> >
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