netdev - Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to power of 2

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Message-ID: <CAJ8uoz1a-71CBCYTd5-F1zsueMq+eu9LUqUsPgQH_SawdO6GEQ@mail.gmail.com>
Date:   Tue, 25 Jan 2022 10:06:13 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>
Subject: Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to
 power of 2

On Mon, Jan 24, 2022 at 8:38 PM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> With the upcoming introduction of batching to XSK data path,
> performance wise it will be the best to have the ring descriptor count
> to be aligned to power of 2.
>
> Check if rings sizes that user is going to attach the XSK socket fulfill

nit: rings -> ring if you are making a v5 for some other reason.

> the condition above. For Tx side, although check is being done against
> the Tx queue and in the end the socket will be attached to the XDP
> queue, it is fine since XDP queues get the ring->count setting from Tx
> queues.

For me, this is fine as it makes the driver simpler and faster. But if
anyone out there is using a non power-of-2 ring size together with the
ice zero-copy driver and wants to keep it that way, now would be a
good time to protest.

Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

> Suggested-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 2388837d6d6c..0350f9c22c62 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -327,6 +327,14 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>         bool if_running, pool_present = !!pool;
>         int ret = 0, pool_failure = 0;
>
> +       if (!is_power_of_2(vsi->rx_rings[qid]->count) ||
> +           !is_power_of_2(vsi->tx_rings[qid]->count)) {
> +               netdev_err(vsi->netdev,
> +                          "Please align ring sizes at idx %d to power of 2\n", qid);
> +               pool_failure = -EINVAL;
> +               goto failure;
> +       }
> +
>         if_running = netif_running(vsi->netdev) && ice_is_xdp_ena_vsi(vsi);
>
>         if (if_running) {
> @@ -349,6 +357,7 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>                         netdev_err(vsi->netdev, "ice_qp_ena error = %d\n", ret);
>         }
>
> +failure:
>         if (pool_failure) {
>                 netdev_err(vsi->netdev, "Could not %sable buffer pool, error = %d\n",
>                            pool_present ? "en" : "dis", pool_failure);
> --
> 2.33.1
>