Re: [PATCH v19] virtio-net: support inner header hash

[Jason Wang <jasowang@redhat.com>]

å 2023/6/28 18:10, Michael S. Tsirkin åé:
> On Wed, Jun 28, 2023 at 11:46:22AM +0800, Jason Wang wrote:
> > On Wed, Jun 28, 2023 at 12:35âAM Heng Qi <hengqi@linux.alibaba.com> wrote:
> > > 1. Currently, a received encapsulated packet has an outer and an inner header, but
> > > the virtio device is unable to calculate the hash for the inner header. The same
> > > flow can traverse through different tunnels, resulting in the encapsulated
> > > packets being spread across multiple receive queues (refer to the figure below).
> > > However, in certain scenarios, we may need to direct these encapsulated packets of
> > > the same flow to a single receive queue. This facilitates the processing
> > > of the flow by the same CPU to improve performance (warm caches, less locking, etc.).
> > >
> > >                 client1                    client2
> > >                    |        +-------+         |
> > >                    +------->|tunnels|<--------+
> > >                             +-------+
> > >                                |  |
> > >                                v  v
> > >                        +-----------------+
> > >                        | monitoring host |
> > >                        +-----------------+
> > >
> > > To achieve this, the device can calculate a symmetric hash based on the inner headers
> > > of the same flow.
> > >
> > > 2. For legacy systems, they may lack entropy fields which modern protocols have in
> > > the outer header, resulting in multiple flows with the same outer header but
> > > different inner headers being directed to the same receive queue. This results in
> > > poor receive performance.
> > >
> > > To address this limitation, inner header hash can be used to enable the device to advertise
> > > the capability to calculate the hash for the inner packet, regaining better receive performance.
> > >
> > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/173
> > > Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> > > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > Reviewed-by: Parav Pandit <parav@nvidia.com>
> > > ---
> > > v18->v19:
> > >          1. Have a single structure instead of two. @Michael S . Tsirkin
> > >          2. Some small rewrites. @Michael S . Tsirkin
> > >          3. Rebase to master.
> > >
> > > v17->v18:
> > >          1. Some rewording suggestions from Michael (Thanks!).
> > >          2. Use 0 to disable inner header hash and remove
> > >             VIRTIO_NET_HASH_TUNNEL_TYPE_NONE.
> > > v16->v17:
> > >          1. Some small rewrites. @Parav Pandit
> > >          2. Add Parav's Reviewed-by tag (Thanks!).
> > >
> > > v15->v16:
> > >          1. Remove the hash_option. In order to delimit the inner header hash and RSS
> > >             configuration, the ability to configure the outer src udp port hash is given
> > >             to RSS. This is orthogonal to inner header hash, which will be done in the
> > >             RSS capability extension topic (considered as an RSS extension together
> > >             with the symmetric toeplitz hash algorithm, etc.). @Parav Pandit @Michael S . Tsirkin
> > >          2. Fix a 'field' typo. @Parav Pandit
> > >
> > > v14->v15:
> > >          1. Add tunnel hash option suggested by @Michael S . Tsirkin
> > >          2. Adjust some descriptions.
> > >
> > > v13->v14:
> > >          1. Move supported_hash_tunnel_types from config space into cvq command. @Parav Pandit
> > I may miss some discussions, but this complicates the provisioning a lot.
> >
> > Having it in the config space, then a type agnostic provisioning
> > through config space + feature bits just works fine.
> >
> > If we move it only via cvq, we need device specific provisioning interface.
> >
> > Thanks
> Yea that's what I said too. Debugging too.  I think we should build a
> consistent solution that allows accessing config space through DMA,
> separately from this effort.  Parav do you think you can live with this
> approach so this specific proposal can move forward?


We can probably go another way, invent a new device configuration space 
capability which fixed size like PCI configuration access capability?

struct virtio_pci_cfg_cap {
ÂÂÂÂÂÂÂ struct virtio_pci_cap cap;
ÂÂÂÂÂÂÂ u8 dev_cfg_data[4]; /* Data for device configuration space 
access. */
};

So it won't grow as the size of device configuration space grows.

Thanks


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