Re: Supporting RSS with DPDK in a VM

[Thomas Monjalon <thomas@monjalon.net>]

Hello,

You can have packets distributed to multiple queues without RSS.

If you really wants to enable the RSS algorithms,
it seems not supported for now with vhost_user.
It can be enabled with vhost running in the kernel:
https://qemu.readthedocs.io/en/latest/devel/ebpf_rss.html


26/07/2023 00:58, Matheus Stolet:
> Hello,
> 
> 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
> 
> 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:
>    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
>