Hi, while running some tests on my Breadbee board, I noticed poor network Tx performance. I had a look at the driver (macb, at91ether variant) and noticed that at91ether_start_xmit() immediately stops the queue after sending a frame and waits for the interrupt to restart the queue, causing a dead time after each packet is sent.
The AT91RM9200 datasheet states that the controller supports two frames, one being sent and the other one being queued, so I performed minimal changes to support this. The transmit performance on my board has increased by 50% on medium-sized packets (HTTP traffic), and with large packets I can now reach line rate. Since this driver is shared by various platforms, I tried my best to isolate and limit the changes as much as possible and I think it's pretty reasonable as-is. I've run extensive tests and couldn't meet any unexpected situation (no stall, overflow nor lockup). There are 3 patches in this series. The first one adds the missing interrupt flag for RM9200 (TBRE, indicating the tx buffer is willing to take a new packet). The second one replaces the single skb with a 2-array and uses only index 0. It does no other change, this is just to prepare the code for the third one. The third one implements the queue. Packets are added at the tail of the queue, the queue is stopped at 2 packets and the interrupt releases 0, 1 or 2 depending on what the transmit status register reports. Thanks, Willy Willy Tarreau (3): macb: add RM9200's interrupt flag TBRE macb: prepare at91 to use a 2-frame TX queue macb: support the two tx descriptors on at91rm9200 drivers/net/ethernet/cadence/macb.h | 10 ++-- drivers/net/ethernet/cadence/macb_main.c | 66 ++++++++++++++++++------ 2 files changed, 56 insertions(+), 20 deletions(-) -- 2.28.0
