linux-kernel - Re: [PATCH net-next] net: systemport: Do not block interrupts in TX reclaim

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Date:   Fri, 24 Jan 2020 17:35:31 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Cc:     kuba@...nel.org, edumazet@...gle.com,
        "David S. Miller" <davem@...emloft.net>,
        "open list:BROADCOM SYSTEMPORT ETHERNET DRIVER" 
        <bcm-kernel-feedback-list@...adcom.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: systemport: Do not block interrupts in TX
 reclaim



On 1/24/20 3:59 PM, Florian Fainelli wrote:
> There is no need to disable interrupts with a spin_lock_irqsave() in
> bcm_sysport_tx_poll() since we are in softIRQ context already. Leave
> interrupts enabled, thus giving a chance for the RX interrupts to be
> processed.
> 
> This now makes bcm_sysport_tx_reclaim() equivalent to
> bcm_sysport_tx_clean(), thus remove the former, and make
> bcm_sysport_tx_reclaim_all() to use the latter.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  drivers/net/ethernet/broadcom/bcmsysport.c | 30 ++++++----------------
>  1 file changed, 8 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c
> index f07ac0e0af59..dfff0657ce8f 100644
> --- a/drivers/net/ethernet/broadcom/bcmsysport.c
> +++ b/drivers/net/ethernet/broadcom/bcmsysport.c
> @@ -925,26 +925,6 @@ static unsigned int __bcm_sysport_tx_reclaim(struct bcm_sysport_priv *priv,
>  	return pkts_compl;
>  }
>  
> -/* Locked version of the per-ring TX reclaim routine */
> -static unsigned int bcm_sysport_tx_reclaim(struct bcm_sysport_priv *priv,
> -					   struct bcm_sysport_tx_ring *ring)
> -{
> -	struct netdev_queue *txq;
> -	unsigned int released;
> -	unsigned long flags;
> -
> -	txq = netdev_get_tx_queue(priv->netdev, ring->index);
> -
> -	spin_lock_irqsave(&ring->lock, flags);
> -	released = __bcm_sysport_tx_reclaim(priv, ring);
> -	if (released)
> -		netif_tx_wake_queue(txq);
> -
> -	spin_unlock_irqrestore(&ring->lock, flags);
> -
> -	return released;
> -}
> -
>  /* Locked version of the per-ring TX reclaim, but does not wake the queue */
>  static void bcm_sysport_tx_clean(struct bcm_sysport_priv *priv,
>  				 struct bcm_sysport_tx_ring *ring)
> @@ -960,9 +940,15 @@ static int bcm_sysport_tx_poll(struct napi_struct *napi, int budget)
>  {
>  	struct bcm_sysport_tx_ring *ring =
>  		container_of(napi, struct bcm_sysport_tx_ring, napi);
> +	struct bcm_sysport_priv *priv = ring->priv;
>  	unsigned int work_done = 0;
>  
> -	work_done = bcm_sysport_tx_reclaim(ring->priv, ring);
> +	spin_lock(&ring->lock);
> +	work_done = __bcm_sysport_tx_reclaim(priv, ring);
> +	if (work_done)
> +		netif_tx_wake_queue(netdev_get_tx_queue(priv->netdev,
> +							ring->index));
> +	spin_unlock(&ring->lock);
>  
>  	if (work_done == 0) {
>  		napi_complete(napi);
> @@ -984,7 +970,7 @@ static void bcm_sysport_tx_reclaim_all(struct bcm_sysport_priv *priv)
>  	unsigned int q;
>  
>  	for (q = 0; q < priv->netdev->num_tx_queues; q++)
> -		bcm_sysport_tx_reclaim(priv, &priv->tx_rings[q]);
> +		bcm_sysport_tx_clean(priv, &priv->tx_rings[q]);
>  }
>  
>  static int bcm_sysport_poll(struct napi_struct *napi, int budget)
> 

I am a bit confused by this patch, the changelog mixes hard and soft irqs.

This driver seems to call bcm_sysport_tx_reclaim_all() from hard irq handler 
(INTRL2_0_TX_RING_FULL condition)

So it looks you need to acquire ring->lock with some _irqsave() variant when
bcm_sysport_tx_poll() is running (from BH context)