netdev - Re: [PATCH net-next 0/2] Introduce XDP_FLAGS_NO

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Date:   Mon, 11 Jan 2021 12:10:22 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Charlie Somerville <charlie@...rlie.bz>, davem@...emloft.net,
        kuba@...nel.org, mst@...hat.com, jasowang@...hat.com
Cc:     netdev@...r.kernel.org, Charlie Somerville <charlie@...rlie.bz>
Subject: Re: [PATCH net-next 0/2] Introduce XDP_FLAGS_NO_TX flag

Charlie Somerville <charlie@...rlie.bz> writes:

> This patch series introduces a new flag XDP_FLAGS_NO_TX which prevents
> the allocation of additional send queues for XDP programs.
>
> Included in this patch series is an implementation of XDP_FLAGS_NO_TX
> for the virtio_net driver. This flag is intended to be advisory - not
> all drivers must implement support for it.
>
> Many virtualised environments only provide enough virtio_net send queues
> for the number of processors allocated to the VM:
>
> # nproc
> 8
> # ethtool --show-channels ens3
> Channel parameters for ens3:
> Pre-set maximums:
> RX:     0
> TX:     0
> Other:      0
> Combined:   8
>
> In this configuration XDP is unusable because the virtio_net driver
> always tries to allocate an extra send queue for each processor - even
> if the XDP the program never uses the XDP_TX functionality.
>
> While XDP_TX is still unavailable in these environments, this new flag
> expands the set of XDP programs that can be used.

I don't think adding a new flag is a good idea. Why can't you just fix
the driver?

-Toke