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From: Vladimir Oltean <olteanv@gmail.com>
To: Kurt Kanzenbach <kurt@linutronix.de>
Cc: Vinicius Costa Gomes <vinicius.gomes@intel.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	devicetree@vger.kernel.org,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Richard Cochran <richardcochran@gmail.com>,
	Kamil Alkhouri <kamil.alkhouri@hs-offenburg.de>,
	ilias.apalodimas@linaro.org
Subject: Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support
Date: Tue, 1 Sep 2020 17:47:55 +0300	[thread overview]
Message-ID: <20200901144755.jd2wnmweywwvkwvl@skbuf> (raw)
In-Reply-To: <87v9gxefzj.fsf@kurt>

On Tue, Sep 01, 2020 at 04:20:00PM +0200, Kurt Kanzenbach wrote:
>
> After giving this a bit more thought, it can be implemented by using
> workqueues only. That ptp time is "cached" anyway the we could just
> periodically check for the base time arrival. That should solve the
> irqsave and the being synchronized problem.
>
> Thanks,
> Kurt

Ok, this sounds simple enough. If the base-time is within 8 seconds of
the current PTP time, then apply the taprio configuration, otherwise
reschedule a delayed workqueue after N seconds (where N has what
value?).

If my math is correct, then N can't simply be the the delta between the
current PTP time and the (base-time minus 8 seconds) value - i.e. just
one schedule_delayed_work - because at large deltas, the PHC frequency
adjustment (+/- 6.25%) starts to matter. At maximum frequency, the PHC
can exceed the monotonic clock of the system by more than 8 seconds in
(8 * 100 / 6.25) = 128 seconds. So if the base-time is in the future by
more than 128 seconds and you plan for a single schedule_delayed_work,
there's a chance that you'll miss the window. And even if you try to
compensate using the current frequency adjustment, that's all that it is
- the current, instantaneous frequency adjustment, not the one from 128
seconds later.

How about N being half that delta? It's not ideal, since there would
need to be log2(delta) reschedules, but at least the error of the first
approximation won't propagate to the next, and the delta will keep
decreasing as time passes, therefore so will the error.

Thanks,
-Vladimir

  reply	other threads:[~2020-09-01 14:48 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-20  8:11 [PATCH v3 0/8] Hirschmann Hellcreek DSA driver Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 1/8] net: dsa: Add tag handling for Hirschmann Hellcreek switches Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 2/8] net: dsa: Add DSA driver " Kurt Kanzenbach
2020-08-24 22:44   ` Andrew Lunn
2020-08-25  9:07     ` Kurt Kanzenbach
2020-08-25 13:56       ` Andrew Lunn
2020-08-25 14:48         ` Kurt Kanzenbach
2020-08-27 10:29           ` Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 3/8] net: dsa: hellcreek: Add PTP clock support Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 4/8] net: dsa: hellcreek: Add support for hardware timestamping Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support Kurt Kanzenbach
2020-08-22 14:39   ` Vladimir Oltean
2020-08-24  6:10     ` Kurt Kanzenbach
2020-08-24 23:45       ` Vinicius Costa Gomes
2020-08-25  9:42         ` Kurt Kanzenbach
2020-08-25 17:58           ` Vinicius Costa Gomes
2020-08-27 10:12             ` Kurt Kanzenbach
2020-08-25  9:46         ` Vladimir Oltean
2020-08-25 10:09           ` Kurt Kanzenbach
2020-08-25 17:33           ` Vinicius Costa Gomes
2020-08-24 22:56   ` Vladimir Oltean
2020-08-25  9:33     ` Kurt Kanzenbach
2020-08-25  9:38       ` Vladimir Oltean
2020-08-25  9:55         ` Kurt Kanzenbach
2020-08-27 16:25           ` Richard Cochran
2020-08-28 12:31             ` Kurt Kanzenbach
2020-08-24 23:57   ` Vinicius Costa Gomes
2020-08-25  9:23     ` Kurt Kanzenbach
2020-08-25  9:32       ` Vladimir Oltean
2020-09-01 14:20         ` Kurt Kanzenbach
2020-09-01 14:47           ` Vladimir Oltean [this message]
2020-08-25 17:50       ` Vinicius Costa Gomes
2020-08-20  8:11 ` [PATCH v3 6/8] net: dsa: hellcreek: Add PTP status LEDs Kurt Kanzenbach
2020-08-24 22:50   ` Andrew Lunn
2020-08-20  8:11 ` [PATCH v3 7/8] dt-bindings: Add vendor prefix for Hirschmann Kurt Kanzenbach
2020-08-20  8:11 ` [PATCH v3 8/8] dt-bindings: net: dsa: Add documentation for Hellcreek switches Kurt Kanzenbach
2020-08-24 22:52   ` Andrew Lunn
2020-08-25 22:28   ` Rob Herring
2020-08-24 21:31 ` [PATCH v3 0/8] Hirschmann Hellcreek DSA driver Jakub Kicinski
2020-08-24 22:02   ` Vladimir Oltean
2020-08-24 22:35     ` David Miller
2020-08-24 22:57       ` Vladimir Oltean
2020-08-25 11:21       ` Kurt Kanzenbach
2020-08-25 17:14         ` Florian Fainelli

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