[xdp-hints] Re: [PATCH bpf-next v6 4/4] igc: Add launch time support to XDP ZC

["Bouska, Zdenek" <zdenek.bouska@siemens.com>]

Hi Siang,

I tested this patch series on 6.13 with Intel I226-LM (rev 04).

I also applied patch "selftests/bpf: Actuate tx_metadata_len in xdp_hw_metadata" [1]
and "selftests/bpf: Enable Tx hwtstamp in xdp_hw_metadata" [2] so that TX timestamps
work.

HW RX-timestamp was small (0.5956 instead of 1737373125.5956):

HW RX-time:   595572448 (sec:0.5956) delta to User RX-time sec:1737373124.9873 (1737373124987318.750 usec)
XDP RX-time:   1737373125582798388 (sec:1737373125.5828) delta to User RX-time sec:0.0001 (92.733 usec)

Igc's raw HW RX-timestamp in front of frame data was overwritten by BPF program on
line 90 in tools/testing/selftests/bpf: meta->hint_valid = 0;

"HW timestamp has been copied into local variable" comment is outdated on
line 2813 in drivers/net/ethernet/intel/igc/igc_main.c after
commit 069b142f5819 igc: Add support for PTP .getcyclesx64() [3].

Workaround is to add unused data to xdp_meta struct:

--- a/tools/testing/selftests/bpf/xdp_metadata.h
+++ b/tools/testing/selftests/bpf/xdp_metadata.h
@@ -49,4 +49,5 @@ struct xdp_meta {
                __s32 rx_vlan_tag_err;
        };
        enum xdp_meta_field hint_valid;
+       __u8 avoid_IGC_TS_HDR_LEN[16];
 };

But Launch time still does not work:

HW Launch-time:   1737374407515922696 (sec:1737374407.5159) delta to HW TX-complete-time sec:-0.9999 (-999923.649 usec)

Command "sudo ethtool -X enp1s0 start 1 equal 1" was in v4 [4] but is not in v6.
Was that intentional? After executing it Launch time feature works:

HW Launch-time:   1737374618088557111 (sec:1737374618.0886) delta to HW TX-complete-time sec:0.0000 (0.012 usec)

Thank you for XDP launch time support!

[1] https://lore.kernel.org/linux-kernel/20241205044258.3155799-1-yoong.siang.song@intel.com/
[2] https://lore.kernel.org/linux-kernel/20241205051936.3156307-1-yoong.siang.song@intel.com/
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=069b142f58196bd9f47b35e493255741e2c663c7
[4] https://lore.kernel.org/linux-kernel/20250106135724.9749-1-yoong.siang.song@intel.com/

Best regards,
Zdenek Bouska

--
Siemens, s.r.o
Foundational Technologies

> -----Original Message-----
> From: Song Yoong Siang <yoong.siang.song@intel.com>
> Sent: Thursday, January 16, 2025 4:54 PM
> To: David S . Miller <davem@davemloft.net>; Eric Dumazet
> <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo Abeni
> <pabeni@redhat.com>; Simon Horman <horms@kernel.org>; Willem de Bruijn
> <willemb@google.com>; Bezdeka, Florian (FT RPD CED OES-DE)
> <florian.bezdeka@siemens.com>; Donald Hunter
> <donald.hunter@gmail.com>; Jonathan Corbet <corbet@lwn.net>; Bjorn
> Topel <bjorn@kernel.org>; Magnus Karlsson <magnus.karlsson@intel.com>;
> Maciej Fijalkowski <maciej.fijalkowski@intel.com>; Jonathan Lemon
> <jonathan.lemon@gmail.com>; Andrew Lunn <andrew+netdev@lunn.ch>;
> Alexei Starovoitov <ast@kernel.org>; Daniel Borkmann
> <daniel@iogearbox.net>; Jesper Dangaard Brouer <hawk@kernel.org>; John
> Fastabend <john.fastabend@gmail.com>; Joe Damato <jdamato@fastly.com>;
> Stanislav Fomichev <sdf@fomichev.me>; Xuan Zhuo
> <xuanzhuo@linux.alibaba.com>; Mina Almasry <almasrymina@google.com>;
> Daniel Jurgens <danielj@nvidia.com>; Song Yoong Siang
> <yoong.siang.song@intel.com>; Andrii Nakryiko <andrii@kernel.org>; Eduard
> Zingerman <eddyz87@gmail.com>; Mykola Lysenko <mykolal@fb.com>;
> Martin KaFai Lau <martin.lau@linux.dev>; Song Liu <song@kernel.org>;
> Yonghong Song <yonghong.song@linux.dev>; KP Singh
> <kpsingh@kernel.org>; Hao Luo <haoluo@google.com>; Jiri Olsa
> <jolsa@kernel.org>; Shuah Khan <shuah@kernel.org>; Alexandre Torgue
> <alexandre.torgue@foss.st.com>; Jose Abreu <joabreu@synopsys.com>;
> Maxime Coquelin <mcoquelin.stm32@gmail.com>; Tony Nguyen
> <anthony.l.nguyen@intel.com>; Przemek Kitszel
> <przemyslaw.kitszel@intel.com>
> Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> doc@vger.kernel.org; bpf@vger.kernel.org; linux-kselftest@vger.kernel.org;
> linux-stm32@st-md-mailman.stormreply.com; linux-arm-
> kernel@lists.infradead.org; intel-wired-lan@lists.osuosl.org; xdp-hints@xdp-
> project.net
> Subject: [PATCH bpf-next v6 4/4] igc: Add launch time support to XDP ZC
> 
> 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)
>   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
> 
> Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
> ---
>  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
> 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
>  	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);
> +}
> +
>  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,
>  	skb->tstamp = ktime_set(0, 0);
>  	launch_time = igc_tx_launchtime(tx_ring, txtime, &first_flag,
> &insert_empty);
> 
> -	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) {
>  		struct igc_metadata_request meta_req;
>  		struct xsk_tx_metadata *meta = NULL;
>  		struct igc_tx_buffer *bi;
> @@ -3004,6 +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);
> @@ -3021,9 +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);
> --
> 2.34.1
>