RE: Supporting RSS with DPDK in a VM

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> -----Original Message-----
> From: Matheus Stolet <mstolet@mpi-sws.org>
> Sent: Tuesday, July 25, 2023 11:59 PM
> To: users@dpdk.org
> Subject: Supporting RSS with DPDK in a VM
> 
> Hello,

Hi  Matheus,

> I am trying to run a DPDK application with RSS enabled so that I can
> have multiple rx queues. This application is running inside a VM. This
> VM is hosted by QEMU using KVM acceleration and OvS with DPDK and
> vhost-user are used in the backend. So to clarify things there are two
> DPDK portions to this. The first is the DPDK portion used by OvS that
> bypasses the host operating system. This is working fine. The other is a
> DPDK application inside the virtual machine that will bypass the guest
> operating system. This is where I am having trouble with.
> 
> When I set rte_eth_conf.rxmode.mq_mode = ETH_MQ_RX_RSS in my application
> I get the following errors:
>    Warning: NIC does not support all requested RSS hash functions.
>    virtio_dev_configure(): RSS support requested but not supported by the
> device
>    Port0 dev_configure = -95

When OVS sees multiple queues negotiated on a vhost port, it will transmit packets to
them. Depending on the "pmd thread" count in OVS, the mapping will be different,
but for best performance it is recommended to match the number of virtq's from
the guest to the number of OVS-pmd-threads on the host.

> I setup my VM in QEMU to have mq=on and queues=10. I also set the number
> of rx_queues when creating the vhost port using ovs to 10. Before
> binding the interface to DPDK, I used ethtool to verify if the network
> interface was actually setup to have multiple queues.
> 
> Running the 'ethtool -l enps02' command yields the following output:

Once you've bound interfaces to DPDK, ethtool no longer works,
and any configuration is reset to when DPDK initializes the port.
Ethtool cannot inspect DPDK ports/applications.

Although this mailing list will likely have experience, the OVS mailing list is likely a better location to
discuss OVS/DPDK/VM performance (I think you've posted there before).

Hope that helps, -Harry


>    Pre-set maximums:
>    RX:             0
>    TX:             0
>    Other:          0
>    Combined:       10
>    Current hardware settings:
>    RX:             0
>    TX:             0
>    Other:          0
>    Combined:       10
> 
>  From my understanding the combined values indicate that the interface
> was properly setup to have multiple queues, so why am I getting the
> unsupported RSS error? Are there other configuration steps that I have
> to take to get this to work? Is RSS with DPDK not supported at all
> inside a VM at the moment? Perhaps the "Port0 dev_configure() = -95"
> error means something else? Without the receive side scaling turned on
> my application is not able to achieve the desired throughput and won't
> scale when I assign more cores to the application.
> 
> Versions:
> VM
> DPDK: 21.11.4
> Kernel: 5.4.0-148-generic
> Distribution: Ubuntu 20.04
> 
> Host
> DPDK: 21.11.4
> QEMU: 8.0.90
> OvS: 3.0.5
> Kernel: 5.15.111.1.amd64-smp
> Distribution: Debian 11