On Monday, January 20, 2025 2:26 PM, Abdul Rahim, Faizal [off-list ref] wrote:

Hi Siang.

On 16/1/2025 11:53 pm, Song Yoong Siang wrote:

quoted

Enable Launch Time Control (LTC) support to XDP zero copy via XDP Tx
metadata framework.

This patch is tested with tools/testing/selftests/bpf/xdp_hw_metadata on
Intel I225-LM Ethernet controller. Below are the test steps and result.

Test Steps:
1. At DUT, start xdp_hw_metadata selftest application:
    $ sudo ./xdp_hw_metadata enp2s0 -l 1000000000 -L 1

2. At Link Partner, send an UDP packet with VLAN priority 1 to port 9091 of
    DUT.

When launch time is set to 1s in the future, the delta between launch time
and transmit hardware timestamp is equal to 0.016us, as shown in result
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)

quoted

   XDP RX-time:   1734578015467651698 (sec:1734578015.4677) delta to User RX-

time sec:0.0001 (80.309 usec)

quoted

   No rx_vlan_tci or rx_vlan_proto, err=-95
   0x562ff5dc8880: ping-pong with csum=561c (want c7dd) csum_start=34

csum_offset=6

quoted

   HW RX-time:   1734578015467548904 (sec:1734578015.4675) delta to HW

Launch-time sec:1.0000 (1000000.000 usec)

quoted

   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)

quoted

   HW TX-complete-time:   1734578016467548920 (sec:1734578016.4675) delta

to User TX-complete-time sec:0.0000 (32.546 usec)

quoted

   XDP RX-time:   1734578015467651698 (sec:1734578015.4677) delta to User TX-

complete-time sec:0.9999 (999929.768 usec)

quoted

   HW RX-time:   1734578015467548904 (sec:1734578015.4675) delta to HW TX-

complete-time sec:1.0000 (1000000.016 usec)

quoted

   0x562ff5dc8880: complete rx idx=132 addr=84110

To be cautious, could we perform a stress test by sending a higher number
of packets with launch time? For example, we could send 200 packets, each
configured with a launch time, and verify that the driver continues to
function correctly afterward.

Hi Faizal,

Thanks for your review comments.
Sure, I can send continuous packets with short interval and share
the result in commit msg.

quoted

Signed-off-by: Song Yoong Siang <redacted>
---
  drivers/net/ethernet/intel/igc/igc_main.c | 78 ++++++++++++++++-------
  1 file changed, 56 insertions(+), 22 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c

b/drivers/net/ethernet/intel/igc/igc_main.c

quoted

index 27872bdea9bd..6857f5f5b4b2 100644

--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c

@@ -1566,6 +1566,26 @@ static bool igc_request_tx_tstamp(struct igc_adapter

*adapter, struct sk_buff *s

quoted

  	return false;
  }

+static void igc_insert_empty_packet(struct igc_ring *tx_ring)
+{
+	struct igc_tx_buffer *empty_info;
+	struct sk_buff *empty;
+	void *data;
+
+	empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
+	empty = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
+	if (!empty)
+		return;
+
+	data = skb_put(empty, IGC_EMPTY_FRAME_SIZE);
+	memset(data, 0, IGC_EMPTY_FRAME_SIZE);
+
+	igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
+
+	if (igc_init_tx_empty_descriptor(tx_ring, empty, empty_info) < 0)
+		dev_kfree_skb_any(empty);
+}
+

The function igc_insert_empty_packet() appears to wrap existing code to
enhance reusability, with no new changes related to enabling launch-time
XDP ZC functionality. If so, could we split this into a separate commit?
This would make it clearer for the reader to distinguish between the
refactoring changes and the new changes related to enabling launch-time XDP
ZC support.

I am ok to split the patch into two. Will do it on next version submission.

quoted

  static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
  				       struct igc_ring *tx_ring)
  {

@@ -1603,26 +1623,8 @@ static netdev_tx_t igc_xmit_frame_ring(struct

sk_buff *skb,

quoted

  	skb->tstamp = ktime_set(0, 0);
  	launch_time = igc_tx_launchtime(tx_ring, txtime, &first_flag,

&insert_empty);

quoted

-	if (insert_empty) {
-		struct igc_tx_buffer *empty_info;
-		struct sk_buff *empty;
-		void *data;
-
-		empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
-		empty = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
-		if (!empty)
-			goto done;
-
-		data = skb_put(empty, IGC_EMPTY_FRAME_SIZE);
-		memset(data, 0, IGC_EMPTY_FRAME_SIZE);
-
-		igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
-
-		if (igc_init_tx_empty_descriptor(tx_ring,
-						 empty,
-						 empty_info) < 0)
-			dev_kfree_skb_any(empty);
-	}
+	if (insert_empty)
+		igc_insert_empty_packet(tx_ring);

  done:
  	/* record the location of the first descriptor for this packet */

@@ -2955,9 +2957,33 @@ 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)

@@ -2980,7 +3006,7 @@ 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--) {
+	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {

Could we add some explanation on what & why the value "4" is used ?

It is because packet with launch time needs 2 descriptors and same goes
for the empty packets. Thus, total need 4 descriptors. I will add detail
explanation. 

Thanks & Regards
Siang