Re: [PATCH iwl-next v3] igb: Retrieve Tx timestamp directly from interrupt for i210

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-02-05 08:54:34 [+0100], Kurt Kanzenbach wrote:
> Retrieve Tx timestamp directly from interrupt handler for i210.
> 
> 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. i210 is often used in
> industrial systems, where timestamp timeouts can be fatal.
> 
> Therefore, fetch the timestamp directly from the interrupt handler.
> 
> The work queue code stays for all other NICs supported by igb.
> 
> Tested on Intel i210 and i350.
> 
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

IMHO this is a compromise with Miroslav where he observed less PTP
timestamps on the i350. While testing I did not get near Miroslav's
difference but there was a small change. I don't understand *why*
because the current workqueue usage reads the timestamp on the same CPU
on which the interrupt occurred. Doing it directly just avoids the
context switch. This feels beneficial.

Sebastian