Re: [PATCH iwl-next v2] igb: Convert Tx timestamping to PTP aux worker

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 22/08/2025 08:28, Kurt Kanzenbach wrote:
> The current implementation uses schedule_work() which is executed by the
> system work queue to retrieve Tx timestamps. This increases latency and can
> lead to timeouts in case of heavy system load.
> 
> Therefore, switch to the PTP aux worker which can be prioritized and pinned
> according to use case. Tested on Intel i210.
> 
>    * igb_ptp_tx_work
> - * @work: pointer to work struct
> + * @ptp: pointer to ptp clock information
>    *
>    * This work function polls the TSYNCTXCTL valid bit to determine when a
>    * timestamp has been taken for the current stored skb.
>    **/
> -static void igb_ptp_tx_work(struct work_struct *work)
> +static long igb_ptp_tx_work(struct ptp_clock_info *ptp)
>   {
> -	struct igb_adapter *adapter = container_of(work, struct igb_adapter,
> -						   ptp_tx_work);
> +	struct igb_adapter *adapter = container_of(ptp, struct igb_adapter,
> +						   ptp_caps);
>   	struct e1000_hw *hw = &adapter->hw;
>   	u32 tsynctxctl;
>   
>   	if (!adapter->ptp_tx_skb)
> -		return;
> +		return -1;
>   
>   	if (time_is_before_jiffies(adapter->ptp_tx_start +
>   				   IGB_PTP_TX_TIMEOUT)) {
> @@ -824,15 +824,17 @@ static void igb_ptp_tx_work(struct work_struct *work)
>   		 */
>   		rd32(E1000_TXSTMPH);
>   		dev_warn(&adapter->pdev->dev, "clearing Tx timestamp hang\n");
> -		return;
> +		return -1;
>   	}
>   
>   	tsynctxctl = rd32(E1000_TSYNCTXCTL);
> -	if (tsynctxctl & E1000_TSYNCTXCTL_VALID)
> +	if (tsynctxctl & E1000_TSYNCTXCTL_VALID) {
>   		igb_ptp_tx_hwtstamp(adapter);
> -	else
> -		/* reschedule to check later */
> -		schedule_work(&adapter->ptp_tx_work);
> +		return -1;
> +	}
> +
> +	/* reschedule to check later */
> +	return 1;

do_aux_work is expected to return delay in jiffies to re-schedule the
work. it would be cleaner to use msec_to_jiffies macros to tell how much
time the driver has to wait before the next try of retrieving the
timestamp. AFAIU, the timestamp may come ASAP in this case, so it's
actually reasonable to request immediate re-schedule of the worker by
returning 0.

>   }