On Wed, 11 Feb 2026 13:08:51 +0100 Kurt Kanzenbach wrote: > On Tue Feb 10 2026, Willem de Bruijn wrote: > > The core issue seems to be that the ptp_tx_work is not scheduled > > quickly enough. I wonder if that is the issue to be fixed. When/why > > is this too slow? > > The igb driver uses schedule_work() for the Tx timestamp retrieval. That > means the ptp_tx_work item is queued to the kernel-global workqueue. In > case there is load on the system, the kworker which handles ptp_tx_work > might be delayed too much, which results in ptp4l timeouts. > > Easy solution would be to tune the priority/affinity of the > kworker. However, we have to figure which kworker it is. Furthermore, > this kworker might handle other things as well, which are not related to > igb timestamping at all. Therefore, tuning the priority of the kworker > is not practical. > > Moving the timestamping in IRQ looked like a good solution, because the > device already signals that the Tx timestamp is available now. No need > to schedule any worker/work at all. So, it'd be very nice if > skb_tstamp_tx() could be called from IRQ context. BTW other drivers like > igc call this function in IRQ context as well. > > Alternative solution for igb is to move from schedule_work() to PTP AUX > worker. That is a dedicated PTP worker thread called ptpX, which could > handle the timestamping. This can be easily tuned with taskset and > chrt. However, there's one difference to the kworker approach: The > kworker always runs on the same CPU, where the IRQ triggered, the AUX > worker not necessarily. This means, Miroslav needs to be aware of this > and tune the AUX worker for his NTP use cases. > > I hope, that makes the motivation for this patch and discussion clear.
Are you concerned about the latency of delivering the TS to the user space app / socket? Or purely reading the TS out of the HW fifo to make space for another packet to be timestamped?
