Hi Andrew, On 07/03/24 10:38 pm, Andrew Lunn wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > >> @@ -55,6 +77,14 @@ >> (OA_TC6_CTRL_MAX_REGISTERS *\ >> OA_TC6_CTRL_REG_VALUE_SIZE) +\ >> OA_TC6_CTRL_IGNORED_SIZE) >> +#define OA_TC6_CHUNK_PAYLOAD_SIZE 64 >> +#define OA_TC6_DATA_HEADER_SIZE 4 >> +#define OA_TC6_CHUNK_SIZE (OA_TC6_DATA_HEADER_SIZE +\ >> + OA_TC6_CHUNK_PAYLOAD_SIZE) >> +#define OA_TC6_TX_SKB_QUEUE_SIZE 100 > > So you keep up to 100 packets in a queue. If use assume typical MTU > size packets, that is 1,238,400 bits. At 10Mbps, that is 120ms of > traffic. That is quite a lot of latency when a high priority packet is > added to the tail of the queue and needs to wait for all the other > packets to be sent first. > > Chunks are 64 bytes. So in practice, you only ever need two > packets. You need to be able to fill a chunk with the final part of > one packet, and the beginning of the next. So i would try using a much > smaller queue size. That will allow Linux queue disciplines to give > you the high priority packets first which you send with low latency. Thanks for the detailed explanation. If I understand you correctly, 1. The tx skb queue size (OA_TC6_TX_SKB_QUEUE_SIZE) should be 2 to avoid the latency when a high priority packet added. 2. Need to implement the handling part of the below case, In case if one packet ends in a chunk and that chunk still having some space left to accommodate some bytes from the next packet if available from network layer. Will implement in the next version. > >> +static void oa_tc6_add_tx_skb_to_spi_buf(struct oa_tc6 *tc6) >> +{ >> + enum oa_tc6_data_start_valid_info start_valid = OA_TC6_DATA_START_INVALID; >> + enum oa_tc6_data_end_valid_info end_valid = OA_TC6_DATA_END_INVALID; >> + __be32 *tx_buf = tc6->spi_data_tx_buf + tc6->spi_data_tx_buf_offset; >> + u16 remaining_length = tc6->tx_skb->len - tc6->tx_skb_offset; >> + u8 *tx_skb_data = tc6->tx_skb->data + tc6->tx_skb_offset; >> + u8 end_byte_offset = 0; >> + u16 length_to_copy; >> + >> + /* Set start valid if the current tx chunk contains the start of the tx >> + * ethernet frame. >> + */ >> + if (!tc6->tx_skb_offset) >> + start_valid = OA_TC6_DATA_START_VALID; >> + >> + /* If the remaining tx skb length is more than the chunk payload size of >> + * 64 bytes then copy only 64 bytes and leave the ongoing tx skb for >> + * next tx chunk. >> + */ >> + length_to_copy = min_t(u16, remaining_length, OA_TC6_CHUNK_PAYLOAD_SIZE); >> + >> + /* Copy the tx skb data to the tx chunk payload buffer */ >> + memcpy(tx_buf + 1, tx_skb_data, length_to_copy); >> + tc6->tx_skb_offset += length_to_copy; > > You probably need a call to skb_linearize() somewhere. You assume the > packet data is contiguous. It can in fact be split into multiple > segments. skb_linearize() will convert it to a single buffer. Ah ok. Then probably I have to add the below code in the oa_tc6_start_xmit() function before adding the skb into the transmit queue. if (skb_linearize(skb)) { dev_kfree_skb_any(skb); tc6->netdev->stats.tx_dropped++; return NETDEV_TX_OK; } > >> +static int oa_tc6_try_spi_transfer(struct oa_tc6 *tc6) >> +{ >> + int ret; >> + >> + while (true) { >> + u16 spi_length = 0; >> + >> + tc6->spi_data_tx_buf_offset = 0; >> + >> + if (tc6->tx_skb || !skb_queue_empty(&tc6->tx_skb_q)) >> + spi_length = oa_tc6_prepare_spi_tx_buf_for_tx_skbs(tc6); >> + >> + if (spi_length == 0) >> + break; >> + >> + ret = oa_tc6_spi_transfer(tc6, OA_TC6_DATA_HEADER, spi_length); >> + if (ret) { >> + netdev_err(tc6->netdev, >> + "SPI data transfer failed. Restart the system: %d\n", >> + ret); > > What does Restart the system mean? Hmm, actually if SPI transfer failed then it can be hardware failure or poor SPI connection. Now I realize that just restarting the system will not help. I will remove "Restart the system:" as it is not the correct info. > >> +static int oa_tc6_spi_thread_handler(void *data) >> +{ >> + struct oa_tc6 *tc6 = data; >> + int ret; >> + >> + while (likely(!kthread_should_stop())) { >> + /* This kthread will be waken up if there is a tx skb */ >> + wait_event_interruptible(tc6->spi_wq, >> + !skb_queue_empty(&tc6->tx_skb_q) || >> + kthread_should_stop()); >> + ret = oa_tc6_try_spi_transfer(tc6); > > Shouldn't you check why you have been woken up? It seems more logical > to test here for kthread_should_stop() rather than have > oa_tc6_try_spi_transfer() handle there is not actually a packet to be > sent. Ok, then I will add the below code before the oa_tc6_try_spi_transfer(). if (kthread_should_stop()) break; Best regards, Parthiban V > > Andrew >