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Date: Wed, 8 May 2013 20:44:41 +1000
From: Peter Jeremy <peter@rulingia.com>
To: Adrian Chadd <adrian@freebsd.org>
Subject: Re: Sawtooth ping RTT on RPi
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On 2013-May-08 03:12:43 -0700, Adrian Chadd <adrian@freebsd.org> wrote:
>yup, that looks like two almost-but-not-in-sync sampling periods (one
>being poll, one being ping) beating against each other.

That seems like a reasonable hypothesis.

>Is the USB stuff being polled?

I'm not sure.  I don't think so.  dmesg says:

dwcotg0: <DWC OTG 2.0 integrated USB controller> mem 0x20980000-0x2099ffff =
irq 17 on simplebus0
usbus0 on dwcotg0
smsc0: <vendor 0x0424 product 0xec00, rev 2.00/2.00, addr 3> on usbus0
ue0: <USB Ethernet> on smsc0

So there's an interrupt available and nothing else is using irq 17.
And systat shows that the interrupt rate on irq 17 goes up with
network traffic (though it idles at ~500 interrupts/sec - which seems
excessive).

--=20
Peter Jeremy

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