[PATCH net-next 0/2] pcnet32: switch to napi_alloc_skb() and napi_gro_receive()

[PATCH net-next 0/2] pcnet32: switch to napi_alloc_skb() and napi_gro_receive()

[Oscar Maes]

Use the newer and more efficient napi_alloc_skb() and napi_gro_receive()
APIs to improve RX throughput.

In my testing this resulted in up to a 25% RX throughput increase in iperf3
tests in both directions.

Oscar Maes (2):
  pcnet32: stop holding device spin lock during napi_complete_done
  pcnet32: switch to napi_alloc_skb() and napi_gro_receive()

 drivers/net/ethernet/amd/pcnet32.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

-- 
2.39.5

[PATCH net-next 1/2] pcnet32: stop holding device spin lock during napi_complete_done

[Oscar Maes]

napi_complete_done may call gro_flush_normal (though not currently, as GRO
is unsupported at the moment), which may result in packet TX. This will
eventually result in calling pcnet32_start_xmit - resulting in a deadlock
while trying to re-acquire the already locked spin lock.

Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
---
 drivers/net/ethernet/amd/pcnet32.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c
index 911808ab13a7..4f3076d4ea34 100644
--- a/drivers/net/ethernet/amd/pcnet32.c
+++ b/drivers/net/ethernet/amd/pcnet32.c
@@ -1407,8 +1407,10 @@ static int pcnet32_poll(struct napi_struct *napi, int budget)
 		pcnet32_restart(dev, CSR0_START);
 		netif_wake_queue(dev);
 	}
+	spin_unlock_irqrestore(&lp->lock, flags);
 
 	if (work_done < budget && napi_complete_done(napi, work_done)) {
+		spin_lock_irqsave(&lp->lock, flags);
 		/* clear interrupt masks */
 		val = lp->a->read_csr(ioaddr, CSR3);
 		val &= 0x00ff;
@@ -1416,9 +1418,9 @@ static int pcnet32_poll(struct napi_struct *napi, int budget)
 
 		/* Set interrupt enable. */
 		lp->a->write_csr(ioaddr, CSR0, CSR0_INTEN);
+		spin_unlock_irqrestore(&lp->lock, flags);
 	}
 
-	spin_unlock_irqrestore(&lp->lock, flags);
 	return work_done;
 }
 
-- 
2.39.5

[PATCH net-next 2/2] pcnet32: switch to napi_alloc_skb() and napi_gro_receive()

[Oscar Maes]

Use the newer and more efficient napi_alloc_skb() and napi_gro_receive()
APIs to improve RX throughput.

Also removes the manual calls to skb_reserve(NET_IP_ALIGN), since
napi_alloc_skb() already does this internally.

Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
---
 drivers/net/ethernet/amd/pcnet32.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c
index 4f3076d4ea34..06d5432bb464 100644
--- a/drivers/net/ethernet/amd/pcnet32.c
+++ b/drivers/net/ethernet/amd/pcnet32.c
@@ -1220,13 +1220,12 @@ static void pcnet32_rx_entry(struct net_device *dev,
 		struct sk_buff *newskb;
 		dma_addr_t new_dma_addr;
 
-		newskb = netdev_alloc_skb(dev, PKT_BUF_SKB);
+		newskb = napi_alloc_skb(&lp->napi, PKT_BUF_SIZE);
 		/*
 		 * map the new buffer, if mapping fails, drop the packet and
 		 * reuse the old buffer
 		 */
 		if (newskb) {
-			skb_reserve(newskb, NET_IP_ALIGN);
 			new_dma_addr = dma_map_single(&lp->pci_dev->dev,
 						      newskb->data,
 						      PKT_BUF_SIZE,
@@ -1251,14 +1250,13 @@ static void pcnet32_rx_entry(struct net_device *dev,
 		} else
 			skb = NULL;
 	} else
-		skb = netdev_alloc_skb(dev, pkt_len + NET_IP_ALIGN);
+		skb = napi_alloc_skb(&lp->napi, pkt_len);
 
 	if (!skb) {
 		dev->stats.rx_dropped++;
 		return;
 	}
 	if (!rx_in_place) {
-		skb_reserve(skb, NET_IP_ALIGN);
 		skb_put(skb, pkt_len);	/* Make room */
 		dma_sync_single_for_cpu(&lp->pci_dev->dev,
 					lp->rx_dma_addr[entry], pkt_len,
@@ -1272,7 +1270,7 @@ static void pcnet32_rx_entry(struct net_device *dev,
 	}
 	dev->stats.rx_bytes += skb->len;
 	skb->protocol = eth_type_trans(skb, dev);
-	netif_receive_skb(skb);
+	napi_gro_receive(&lp->napi, skb);
 	dev->stats.rx_packets++;
 }
 
-- 
2.39.5

Re: [PATCH net-next 1/2] pcnet32: stop holding device spin lock during napi_complete_done

[Andrew Lunn]

On Wed, May 20, 2026 at 08:33:28AM +0200, Oscar Maes wrote:
> napi_complete_done may call gro_flush_normal (though not currently, as GRO
> is unsupported at the moment), which may result in packet TX. This will
> eventually result in calling pcnet32_start_xmit - resulting in a deadlock
> while trying to re-acquire the already locked spin lock.

Please continue to commit message with something like:

  It is safe to release the spinlock, because it is protecting X,
  which is not modified during the time the spinlock is released.

You need to convince us this is safe.


    Andrew

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