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

[Stanislav Fomichev <stfomichev@gmail.com>]

On 03/25, Samiullah Khawaja 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@google.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;
>  }

Can we move this part to a different place? __xsk_rcv maybe? So it
doesn't trigger for the zc case where napi is resolved at bind time.