netdev - Re: [RFC PATCH 2/3] veth: make queues nr configurable via kernel module params

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Date:   Fri, 09 Jul 2021 12:24:48 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC PATCH 2/3] veth: make queues nr configurable via kernel
 module params

Paolo Abeni <pabeni@...hat.com> writes:

> This allows configuring the number of tx and rx queues at
> module load time. A single module parameter controls
> both the default number of RX and TX queues created
> at device registration time.
>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>  drivers/net/veth.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 10360228a06a..787b4ad2cc87 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -27,6 +27,11 @@
>  #include <linux/bpf_trace.h>
>  #include <linux/net_tstamp.h>
>  
> +static int queues_nr	= 1;
> +
> +module_param(queues_nr, int, 0644);
> +MODULE_PARM_DESC(queues_nr, "Max number of RX and TX queues (default = 1)");

Adding new module parameters is generally discouraged. Also, it's sort
of a cumbersome API that you'll have to set this first, then re-create
the device, and then use channels to get the number you want.

So why not just default to allocating num_possible_cpus() number of
queues? Arguably that is the value that makes the most sense from a
scalability point of view anyway, but if we're concerned about behaviour
change (are we?), we could just default real_num_*_queues to 1, so that
the extra queues have to be explicitly enabled by ethtool?

-Toke