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