[xdp-hints] Re: [PATCH bpf-next v7 5/5] igc: Add launch time support to XDP ZC

["Abdul Rahim, Faizal" <faizal.abdul.rahim@linux.intel.com>]

On 4/2/2025 8:49 am, Song Yoong Siang wrote:
> Enable Launch Time Control (LTC) support for XDP zero copy via XDP Tx
> metadata framework.
> 
> This patch has been tested with tools/testing/selftests/bpf/xdp_hw_metadata
> on Intel I225-LM Ethernet controller. Below are the test steps and result.
> 
> Test 1: Send a single packet with the launch time set to 1 s in the future.
> 
> Test steps:
> 1. On the DUT, start the xdp_hw_metadata selftest application:
>     $ sudo ./xdp_hw_metadata enp2s0 -l 1000000000 -L 1
> 
> 2. On the Link Partner, send a UDP packet with VLAN priority 1 to port 9091
>     of the DUT.
> 
> Result:
> When the launch time is set to 1 s in the future, the delta between the
> launch time and the transmit hardware timestamp is 0.016 us, as shown in
> printout of the xdp_hw_metadata application below.
>    0x562ff5dc8880: rx_desc[4]->addr=84110 addr=84110 comp_addr=84110 EoP
>    rx_hash: 0xE343384 with RSS type:0x1
>    HW RX-time:   1734578015467548904 (sec:1734578015.4675)
>                  delta to User RX-time sec:0.0002 (183.103 usec)
>    XDP RX-time:   1734578015467651698 (sec:1734578015.4677)
>                   delta to User RX-time sec:0.0001 (80.309 usec)
>    No rx_vlan_tci or rx_vlan_proto, err=-95
>    0x562ff5dc8880: ping-pong with csum=561c (want c7dd)
>                    csum_start=34 csum_offset=6
>    HW RX-time:   1734578015467548904 (sec:1734578015.4675)
>                  delta to HW Launch-time sec:1.0000 (1000000.000 usec)
>    0x562ff5dc8880: complete tx idx=4 addr=4018
>    HW Launch-time:   1734578016467548904 (sec:1734578016.4675)
>                      delta to HW TX-complete-time sec:0.0000 (0.016 usec)
>    HW TX-complete-time:   1734578016467548920 (sec:1734578016.4675)
>                           delta to User TX-complete-time sec:0.0000
>                           (32.546 usec)
>    XDP RX-time:   1734578015467651698 (sec:1734578015.4677)
>                   delta to User TX-complete-time sec:0.9999
>                   (999929.768 usec)
>    HW RX-time:   1734578015467548904 (sec:1734578015.4675)
>                  delta to HW TX-complete-time sec:1.0000 (1000000.016 usec)
>    0x562ff5dc8880: complete rx idx=132 addr=84110
> 
> Test 2: Send 1000 packets with a 10 ms interval and the launch time set to
>          500 us in the future.
> 
> Test steps:
> 1. On the DUT, start the xdp_hw_metadata selftest application:
>     $ sudo chrt -f 99 ./xdp_hw_metadata enp2s0 -l 500000 -L 1 > \
>       /dev/shm/result.log
> 
> 2. On the Link Partner, send 1000 UDP packets with a 10 ms interval and
>     VLAN priority 1 to port 9091 of the DUT.
> 
> Result:
> When the launch time is set to 500 us in the future, the average delta
> between the launch time and the transmit hardware timestamp is 0.016 us,
> as shown in the analysis of /dev/shm/result.log below. The XDP launch time
> works correctly in sending 1000 packets continuously.
>    Min delta: 0.005 us
>    Avr delta: 0.016 us
>    Max delta: 0.031 us
>    Total packets forwarded: 1000
> 
> Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
> ---
>   drivers/net/ethernet/intel/igc/igc_main.c | 42 +++++++++++++++++++++--
>   1 file changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index c3edd8bcf633..535d340c71c9 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -2951,9 +2951,33 @@ static u64 igc_xsk_fill_timestamp(void *_priv)
>   	return *(u64 *)_priv;
>   }
>   
> +static void igc_xsk_request_launch_time(u64 launch_time, void *_priv)
> +{
> +	struct igc_metadata_request *meta_req = _priv;
> +	struct igc_ring *tx_ring = meta_req->tx_ring;
> +	__le32 launch_time_offset;
> +	bool insert_empty = false;
> +	bool first_flag = false;
> +
> +	if (!tx_ring->launchtime_enable)
> +		return;
> +
> +	launch_time_offset = igc_tx_launchtime(tx_ring,
> +					       ns_to_ktime(launch_time),
> +					       &first_flag, &insert_empty);
> +	if (insert_empty) {
> +		igc_insert_empty_packet(tx_ring);
> +		meta_req->tx_buffer =
> +			&tx_ring->tx_buffer_info[tx_ring->next_to_use];
> +	}
> +
> +	igc_tx_ctxtdesc(tx_ring, launch_time_offset, first_flag, 0, 0, 0);
> +}
> +
>   const struct xsk_tx_metadata_ops igc_xsk_tx_metadata_ops = {
>   	.tmo_request_timestamp		= igc_xsk_request_timestamp,
>   	.tmo_fill_timestamp		= igc_xsk_fill_timestamp,
> +	.tmo_request_launch_time	= igc_xsk_request_launch_time,
>   };
>   
>   static void igc_xdp_xmit_zc(struct igc_ring *ring)
> @@ -2976,7 +3000,13 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>   	ntu = ring->next_to_use;
>   	budget = igc_desc_unused(ring);
>   
> -	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget--) {
> +	/* Packets with launch time require one data descriptor and one context
> +	 * descriptor. When the launch time falls into the next Qbv cycle, we
> +	 * may need to insert an empty packet, which requires two more
> +	 * descriptors. Therefore, to be safe, we always ensure we have at least
> +	 * 4 descriptors available.
> +	 */
> +	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {
>   		struct igc_metadata_request meta_req;
>   		struct xsk_tx_metadata *meta = NULL;
>   		struct igc_tx_buffer *bi;
> @@ -3000,6 +3030,12 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>   		xsk_tx_metadata_request(meta, &igc_xsk_tx_metadata_ops,
>   					&meta_req);
>   
> +		/* xsk_tx_metadata_request() may have updated next_to_use */
> +		ntu = ring->next_to_use;
> +
> +		/* xsk_tx_metadata_request() may have updated Tx buffer info */
> +		bi = meta_req.tx_buffer;
> +
>   		tx_desc = IGC_TX_DESC(ring, ntu);
>   		tx_desc->read.cmd_type_len = cpu_to_le32(meta_req.cmd_type);
>   		tx_desc->read.olinfo_status = cpu_to_le32(olinfo_status);
> @@ -3017,9 +3053,11 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>   		ntu++;
>   		if (ntu == ring->count)
>   			ntu = 0;
> +
> +		ring->next_to_use = ntu;
> +		budget = igc_desc_unused(ring);
>   	}
>   
> -	ring->next_to_use = ntu;
>   	if (tx_desc) {
>   		igc_flush_tx_descriptors(ring);
>   		xsk_tx_release(pool);

Reviewed-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>