From: Sven Van Asbroeck <thesve...@gmail.com>
Even if the rx ring is completely full, and there is more rx data
waiting on the chip, the rx napi poll fn will never run more than
once - it will always immediately bail out and re-enable interrupts.
Which results in ping-pong between napi and interrupt.
This defeats the purpose of napi, and is bad for performance.
Fix by addressing two separate issues:
1. Ensure the rx napi poll fn always updates the rx ring tail
when returning, even when not re-enabling interrupts.
2. Up to half of elements in a full rx ring are extension
frames, which do not generate any skbs. Limit the default
napi weight to the smallest no. of skbs that can be generated
by a full rx ring.
Tested-by: Sven Van Asbroeck <thesve...@gmail.com> # lan7430
Signed-off-by: Sven Van Asbroeck <thesve...@gmail.com>
---
Tree: git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git # 905b2032fa42
To: Bryan Whitehead <bryan.whiteh...@microchip.com>
To: Microchip Linux Driver Support <unglinuxdri...@microchip.com>
To: "David S. Miller" <da...@davemloft.net>
To: Jakub Kicinski <k...@kernel.org>
Cc: Andrew Lunn <and...@lunn.ch>
Cc: net...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
drivers/net/ethernet/microchip/lan743x_main.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/microchip/lan743x_main.c
b/drivers/net/ethernet/microchip/lan743x_main.c
index 87b6c59a1e03..ebb5e0bc516b 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -2260,10 +2260,11 @@ static int lan743x_rx_napi_poll(struct napi_struct
*napi, int weight)
INT_BIT_DMA_RX_(rx->channel_number));
}
+done:
/* update RX_TAIL */
lan743x_csr_write(adapter, RX_TAIL(rx->channel_number),
rx_tail_flags | rx->last_tail);
-done:
+
return count;
}
@@ -2405,9 +2406,15 @@ static int lan743x_rx_open(struct lan743x_rx *rx)
if (ret)
goto return_error;
+ /* up to half of elements in a full rx ring are
+ * extension frames. these do not generate skbs.
+ * to prevent napi/interrupt ping-pong, limit default
+ * weight to the smallest no. of skbs that can be
+ * generated by a full rx ring.
+ */
netif_napi_add(adapter->netdev,
&rx->napi, lan743x_rx_napi_poll,
- rx->ring_size - 1);
+ (rx->ring_size - 1) / 2);
lan743x_csr_write(adapter, DMAC_CMD,
DMAC_CMD_RX_SWR_(rx->channel_number));
--
2.17.1
