linux-kernel - Re: [PATCH v2 1/2] net: ravb: Always process TX descriptor ring

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Date: Wed, 3 Apr 2024 09:09:32 +0530
From: Ratheesh Kannoth <rkannoth@...vell.com>
To: Paul Barker <paul.barker.ct@...renesas.com>
CC: Sergey Shtylyov <s.shtylyov@....ru>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Niklas
 Söderlund <niklas.soderlund+renesas@...natech.se>,
        <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] net: ravb: Always process TX descriptor ring

On 2024-04-02 at 20:23:04, Paul Barker (paul.barker.ct@...renesas.com) wrote:
> The TX queue should be serviced each time the poll function is called,
> even if the full RX work budget has been consumed. This prevents
> starvation of the TX queue when RX bandwidth usage is high.
>
> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
> ---
> Changes from v1:
>   * Use the correct 'Fixes' tag.
>   * Call the new variable 'unmask' and drop the unnecessary initializer,
>     as requested by Sergey.
>
>  drivers/net/ethernet/renesas/ravb_main.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index d1be030c8848..48803050abdb 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -1324,12 +1324,12 @@ static int ravb_poll(struct napi_struct *napi, int budget)
>  	int q = napi - priv->napi;
>  	int mask = BIT(q);
>  	int quota = budget;
> +	bool unmask;
>
>  	/* Processing RX Descriptor Ring */
>  	/* Clear RX interrupt */
>  	ravb_write(ndev, ~(mask | RIS0_RESERVED), RIS0);
> -	if (ravb_rx(ndev, &quota, q))
> -		goto out;
> +	unmask = !ravb_rx(ndev, &quota, q);
>
>  	/* Processing TX Descriptor Ring */
AFAIU, TX is processed without any budget. This wont result in rx work starvation if
TX traffic is more ?

>  	spin_lock_irqsave(&priv->lock, flags);
> @@ -1339,6 +1339,9 @@ static int ravb_poll(struct napi_struct *napi, int budget)
>  	netif_wake_subqueue(ndev, q);
>  	spin_unlock_irqrestore(&priv->lock, flags);
>
> +	if (!unmask)
> +		goto out;
> +
>  	napi_complete(napi);
>
>  	/* Re-enable RX/TX interrupts */
>
> base-commit: ea2a1cfc3b2019bdea6324acd3c03606b60d71ad
> --
> 2.39.2
>