linux-kernel - RE: [PATCH iwl-next,v2 2/2] igc: Add Tx hardware timestamp request for AF

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Date: Fri, 01 Mar 2024 09:54:34 -0800
From: John Fastabend <john.fastabend@...il.com>
To: Song Yoong Siang <yoong.siang.song@...el.com>, 
 Jesse Brandeburg <jesse.brandeburg@...el.com>, 
 Tony Nguyen <anthony.l.nguyen@...el.com>, 
 "David S . Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 Jesper Dangaard Brouer <hawk@...nel.org>, 
 John Fastabend <john.fastabend@...il.com>, 
 Stanislav Fomichev <sdf@...gle.com>, 
 Vinicius Costa Gomes <vinicius.gomes@...el.com>, 
 Florian Bezdeka <florian.bezdeka@...mens.com>, 
 Andrii Nakryiko <andrii@...nel.org>, 
 Eduard Zingerman <eddyz87@...il.com>, 
 Mykola Lysenko <mykolal@...com>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 KP Singh <kpsingh@...nel.org>, 
 Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, 
 Shuah Khan <shuah@...nel.org>
Cc: intel-wired-lan@...ts.osuosl.org, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 xdp-hints@...-project.net
Subject: RE: [PATCH iwl-next,v2 2/2] igc: Add Tx hardware timestamp request
 for AF_XDP zero-copy packet

Song Yoong Siang wrote:
> This patch adds support to per-packet Tx hardware timestamp request to
> AF_XDP zero-copy packet via XDP Tx metadata framework. Please note that
> user needs to enable Tx HW timestamp capability via igc_ioctl() with
> SIOCSHWTSTAMP cmd before sending xsk Tx hardware timestamp request.
> 
> Same as implementation in RX timestamp XDP hints kfunc metadata, Timer 0
> (adjustable clock) is used in xsk Tx hardware timestamp. i225/i226 have
> four sets of timestamping registers. Both *skb and *xsk_tx_buffer pointers
> are used to indicate whether the timestamping register is already occupied.
> 
> Furthermore, a boolean variable named xsk_pending_ts is used to hold the
> transmit completion until the tx hardware timestamp is ready. This is
> because, for i225/i226, the timestamp notification event comes some time
> after the transmit completion event. The driver will retrigger hardware irq
> to clean the packet after retrieve the tx hardware timestamp.
> 
> Besides, xsk_meta is added into struct igc_tx_timestamp_request as a hook
> to the metadata location of the transmit packet. When the Tx timestamp
> interrupt is fired, the interrupt handler will copy the value of Tx hwts
> into metadata location via xsk_tx_metadata_complete().
> 
> Co-developed-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
> Signed-off-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
> Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
> ---

[...]

>  
> +static void igc_xsk_request_timestamp(void *_priv)
> +{
> +	struct igc_metadata_request *meta_req = _priv;
> +	struct igc_ring *tx_ring = meta_req->tx_ring;
> +	struct igc_tx_timestamp_request *tstamp;
> +	u32 tx_flags = IGC_TX_FLAGS_TSTAMP;
> +	struct igc_adapter *adapter;
> +	unsigned long lock_flags;
> +	bool found = false;
> +	int i;
> +
> +	if (test_bit(IGC_RING_FLAG_TX_HWTSTAMP, &tx_ring->flags)) {
> +		adapter = netdev_priv(tx_ring->netdev);
> +
> +		spin_lock_irqsave(&adapter->ptp_tx_lock, lock_flags);
> +
> +		/* Search for available tstamp regs */
> +		for (i = 0; i < IGC_MAX_TX_TSTAMP_REGS; i++) {
> +			tstamp = &adapter->tx_tstamp[i];
> +
> +			if (tstamp->skb)
> +				continue;
> +
> +			found = true;
> +			break;

Not how I would have written this loop construct seems a bit odd
to default break but it works.

> +		}
> +
> +		/* Return if no available tstamp regs */
> +		if (!found) {
> +			adapter->tx_hwtstamp_skipped++;
> +			spin_unlock_irqrestore(&adapter->ptp_tx_lock,
> +					       lock_flags);
> +			return;
> +		}

[...]

>  
> +static void igc_ptp_free_tx_buffer(struct igc_adapter *adapter,
> +				   struct igc_tx_timestamp_request *tstamp)
> +{
> +	if (tstamp->buffer_type == IGC_TX_BUFFER_TYPE_XSK) {
> +		/* Release the transmit completion */
> +		tstamp->xsk_tx_buffer->xsk_pending_ts = false;
> +		tstamp->xsk_tx_buffer = NULL;
> +		tstamp->buffer_type = 0;
> +
> +		/* Trigger txrx interrupt for transmit completion */
> +		igc_xsk_wakeup(adapter->netdev, tstamp->xsk_queue_index, 0);

Just curious because I didn't find it. Fairly sure I just need to look more,
but don't you want to still 'tstamp->skb = NULL' in this path somewhere?
It looks like triggering the tx interrupt again with buffer_type == 0 wouldn't
do the null.

I suspect I just missed it.