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Date:   Wed, 9 Dec 2020 08:41:05 -0700
From:   David Ahern <>
To:     Jesper Dangaard Brouer <>,
        Maciej Fijalkowski <>
Cc:     John Fastabend <>,
        Daniel Borkmann <>,
        Toke Høiland-Jørgensen <>,,,,,,,,,,,,,,,
        Marek Majtyka <>
Subject: Re: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set

On 12/9/20 4:52 AM, Jesper Dangaard Brouer wrote:
>>> still load and either share queues across multiple cores or restirct
>>> down to a subset of CPUs.  
>> And that's the missing piece of logic, I suppose.
>>> Do you need 192 cores for a 10gbps nic, probably not.  
>> Let's hear from Jesper :p
> LOL - of-cause you don't need 192 cores.  With XDP I will claim that
> you only need 2 cores (with high GHz) to forward 10gbps wirespeed small
> packets.

You don't need 192 for 10G on Rx. However, if you are using XDP_REDIRECT
from VM tap devices the next device (presumably the host NIC) does need
to be able to handle the redirect.

My personal experience with this one is mlx5/ConnectX4-LX with a limit
of 63 queues and a server with 96 logical cpus. If the vhost thread for
the tap device runs on a cpu that does not have an XDP TX Queue, the
packet is dropped. This is a really bizarre case to debug as some
packets go out fine while others are dropped.

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