netdev - Re: [PATCH net-next] xsk: Bring back busy polling support in XDP

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Message-ID: <CAAywjhSEjaSgt7fCoiqJiMufGOi=oxa164_vTfk+3P43H60qwQ@mail.gmail.com>
Date: Tue, 25 Mar 2025 09:24:30 -0700
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, almasrymina@...gle.com, 
	willemb@...gle.com, jdamato@...tly.com, mkarsten@...terloo.ca
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next] xsk: Bring back busy polling support in XDP_COPY

On Mon, Mar 24, 2025 at 9:43 PM Samiullah Khawaja <skhawaja@...gle.com> wrote:
>
> Commit 5ef44b3cb43b ("xsk: Bring back busy polling support") fixed the
> busy polling support in xsk for XDP_ZEROCOPY after it was broken in
> commit 86e25f40aa1e ("net: napi: Add napi_config"). The busy polling
> support with XDP_COPY remained broken since the napi_id setup in
> xsk_rcv_check was removed.
>
> Bring back the setup of napi_id for XDP_COPY so socket level SO_BUSYPOLL
> can be used to poll the underlying napi.
>
> Tested using AF_XDP support in virtio-net by running the xsk_rr AF_XDP
> benchmarking tool shared here:
> https://lore.kernel.org/all/20250320163523.3501305-1-skhawaja@google.com/T/
>
> Enabled socket busy polling using following commands in qemu,
>
> ```
> sudo ethtool -L eth0 combined 1
> sudo ethtool -G eth0 rx 1024
> echo 400 | sudo tee /proc/sys/net/core/busy_read
> echo 100 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs
> echo 15000   | sudo tee /sys/class/net/eth0/gro_flush_timeout
> ```
>
> Fixes: 5ef44b3cb43b ("xsk: Bring back busy polling support")
> Fixes: 86e25f40aa1e ("net: napi: Add napi_config")
> Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>
> ---
>  net/xdp/xsk.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index e5d104ce7b82..de8bf97b2cb9 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -310,6 +310,18 @@ static bool xsk_is_bound(struct xdp_sock *xs)
>         return false;
>  }
>
> +static void __xsk_mark_napi_id_once(struct sock *sk, struct net_device *dev, u32 qid)
> +{
> +       struct netdev_rx_queue *rxq;
> +
> +       if (qid >= dev->real_num_rx_queues)
> +               return;
> +
> +       rxq = __netif_get_rx_queue(dev, qid);
> +       if (rxq->napi)
> +               __sk_mark_napi_id_once(sk, rxq->napi->napi_id);
> +}
> +
>  static int xsk_rcv_check(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
>  {
>         if (!xsk_is_bound(xs))
> @@ -323,6 +335,7 @@ static int xsk_rcv_check(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
>                 return -ENOSPC;
>         }
>
> +       __xsk_mark_napi_id_once(&xs->sk, xs->dev, xs->queue_id);
>         return 0;
>  }
>
> @@ -1300,13 +1313,8 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>         xs->queue_id = qid;
>         xp_add_xsk(xs->pool, xs);
>
> -       if (xs->zc && qid < dev->real_num_rx_queues) {
> -               struct netdev_rx_queue *rxq;
> -
> -               rxq = __netif_get_rx_queue(dev, qid);
> -               if (rxq->napi)
> -                       __sk_mark_napi_id_once(sk, rxq->napi->napi_id);
> -       }
> +       if (xs->zc)
> +               __xsk_mark_napi_id_once(sk, dev, qid);
>
>  out_unlock:
>         if (err) {
> --
> 2.49.0.395.g12beb8f557-goog
>

The original commit 5ef44b3cb43b ("xsk: Bring back busy polling
support") has landed in 6.13 so I will revise this and resend it to
the net. Thanks