netdev - Re: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set

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Date:   Wed, 09 Dec 2020 09:15:41 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     David Ahern <dsahern@...il.com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        alardam@...il.com, magnus.karlsson@...el.com,
        bjorn.topel@...el.com, andrii.nakryiko@...il.com, kuba@...nel.org,
        ast@...nel.org, netdev@...r.kernel.org, davem@...emloft.net,
        hawk@...nel.org, jonathan.lemon@...il.com, bpf@...r.kernel.org,
        jeffrey.t.kirsher@...el.com, maciejromanfijalkowski@...il.com,
        intel-wired-lan@...ts.osuosl.org,
        Marek Majtyka <marekx.majtyka@...el.com>
Subject: Re: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set

On Wed, 2020-12-09 at 08:41 -0700, David Ahern wrote:
> 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

This limit was removed from mlx5
https://patchwork.ozlabs.org/project/netdev/patch/20200107191335.12272-5-saeedm@mellanox.com/
Note: you still need to use ehttool to increase from 64 to 128 or 96 in
your case.

> 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.

I agree, the user experience horrible.