linux-kernel - Re: [PATCH net] r8152: avoid the driver drops a lot of packets

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Message-ID: <32c71d3245127b4aa02b8abd75edcb8f5767e966.camel@redhat.com>
Date:   Tue, 05 Sep 2023 12:10:57 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Hayes Wang <hayeswang@...ltek.com>, kuba@...nel.org,
        davem@...emloft.net
Cc:     netdev@...r.kernel.org, nic_swsd@...ltek.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH net] r8152: avoid the driver drops a lot of packets

Hello,

On Mon, 2023-09-04 at 20:17 +0800, Hayes Wang wrote:
> Stop submitting rx, if the driver queue more than 256 packets.
> 
> If the hardware is more fast than the software, the driver would start
> queuing the packets. And, the driver starts dropping the packets, if it
> queues more than 1000 packets.
> 
> Increase the weight of NAPI could improve the situation. However, the
> weight has been changed to 64, so we have to stop submitting rx when the
> driver queues too many packets. Then,the device may send the pause frame
> to slow down the receiving, when the FIFO of the device is full.
> 
> Fixes: cf74eb5a5bc8 ("eth: r8152: try to use a normal budget")
> Signed-off-by: Hayes Wang <hayeswang@...ltek.com>
> ---
>  drivers/net/usb/r8152.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> index 332c853ca99b..b5ed55938b1c 100644
> --- a/drivers/net/usb/r8152.c
> +++ b/drivers/net/usb/r8152.c
> @@ -2484,10 +2484,6 @@ static int rx_bottom(struct r8152 *tp, int budget)
>  			unsigned int pkt_len, rx_frag_head_sz;
>  			struct sk_buff *skb;
>  
> -			/* limit the skb numbers for rx_queue */
> -			if (unlikely(skb_queue_len(&tp->rx_queue) >= 1000))
> -				break;
> -

Dropping this check looks dangerous to me. What if pause frames are
disabled on the other end or dropped? It looks like this would cause
unlimited memory consumption?!?

If this limit is not supposed to be reached under normal conditions,
perhaps is worthy changing it into a WARN_ON_ONCE()?

Thanks!

Paolo