netdev - Re: [Intel-wired-lan] [PATCH iwl-next] igb: Retrieve Tx timestamp directly from interrupt

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Message-ID: <aKcycAXlKfSxxhZ3@localhost>
Date: Thu, 21 Aug 2025 16:51:28 +0200
From: Miroslav Lichvar <mlichvar@...hat.com>
To: Kurt Kanzenbach <kurt@...utronix.de>
Cc: Jacob Keller <jacob.e.keller@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"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>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH iwl-next] igb: Retrieve Tx timestamp
 directly from interrupt

On Thu, Aug 21, 2025 at 04:08:02PM +0200, Kurt Kanzenbach wrote:
> On Thu Aug 21 2025, Miroslav Lichvar wrote:
> >> >> Without the patch:
> >> >> NTP daemon TX timestamps   : 35835
> >> >> NTP kernel TX timestamps   : 1410956
> >> >> NTP hardware TX timestamps : 581575            
> >> >> 
> >> >> With the patch:
> >> >> NTP daemon TX timestamps   : 476908
> >> >> NTP kernel TX timestamps   : 646146
> >> >> NTP hardware TX timestamps : 412095

> > With the new patch at 200000 requests per second:
> > NTP daemon TX timestamps   : 192404
> > NTP kernel TX timestamps   : 1318971
> > NTP hardware TX timestamps : 418805

> Here's what I can see in the traces: In the current implementation, the
> kworker runs directly after the IRQ on the *same* CPU. With the AUX
> worker approach the kthread can be freely distributed to any other
> CPU. This in turn involves remote wakeups etc.
> 
> You could try to pin the PTP AUX worker (e.g. called ptp0) with taskset
> to the same CPU where the TS IRQs are processed. That might help to get
> the old behavior back. Adjusting the priority is not necessary, both the
> kworker and AUX thread run with 120 (SCHED_OTHER, nice value 0) by
> default.

Yes, that helps!

The server timestamping stats now show:
NTP daemon TX timestamps   : 32902
NTP kernel TX timestamps   : 1479293
NTP hardware TX timestamps : 520146

And the maximum response rate is only about 2-3% lower, so that looks
good to me.

Thanks,

-- 
Miroslav Lichvar