[MLX5] Tx scheduling strange behavior on connectx6DX

[MLX5] Tx scheduling strange behavior on connectx6DX

[Antoine POLLENUS]

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Hello,

I'm trying to use the TX scheduling feature on a ConnectX-6Dx with latest firmware and 21.11 version of DPDK.
But I see some strange behavior.

When I advise the nic with the timestamp in the dynamic mbuf field the packet go out way too early.

Time I want : 1662385925567940000
Received time : 1662385925469600500

The time I want is 100ms in the future of when calling rte_tx_burst.

When looking at the xstats I see no packet in the past no packets in a too long future. But as shown below I see tx_pp_sync_lost, tx_pp_missed_interrupt_errors, tx_pp_rearm_queue_errors

Which seems to be a bad behavior.

tx_good_packets:83160
tx_good_bytes:528950026
tx_q0_packets:83160
tx_q0_bytes:528950026
rx_multicast_packets:64
rx_multicast_bytes:6318
tx_multicast_packets:66772
tx_multicast_bytes:94358324
tx_phy_packets:66750
rx_phy_packets:64
tx_phy_bytes:94595646
rx_phy_bytes:6318
tx_pp_missed_interrupt_errors:2
tx_pp_rearm_queue_errors:2
tx_pp_jitter:40
tx_pp_sync_lost:1

For information my tx_pp is set to 500. My NIC is locked on PTP with ptp4l and phc2sys is used to synchronize the system clock

Another strange thing is that the data rate and the pacing seams ok but every packets are too early but constant.

Sometimes I also see the tx_pp_wander going really high at the start of the transition ( more than 30000000).

I tried with testpmd and I see no error so it's seams the problem is something I do that cause the issue.

My question is what could cause the errors I see in the xstats, I think it's the key to my problem.

Could you also explain a bit what those tx_pp xstats represent because even when looking at the source code it doesn't seems clear.

Thank you in advance for your help.

Regards,

Antoine Pollenus




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