From owner-freebsd-net  Fri Oct 18 10:38:28 2002
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Date: Fri, 18 Oct 2002 10:38:25 -0700
From: Luigi Rizzo <rizzo@icir.org>
To: Petri Helenius <pete@he.iki.fi>
Cc: Jim McGrath <jimmcgra@bellatlantic.net>,
	Lars Eggert <larse@ISI.EDU>, freebsd-net@FreeBSD.ORG,
	freebsdnic@mailbox.cps.intel.com
Subject: Re: ENOBUFS
Message-ID: <20021018103825.B82982@carp.icir.org>
References: <NDBBKKEELKBCJJBEGDECCEHJCGAA.jimmcgra@bellatlantic.net> <00b001c276ba$1533dbf0$3500080a@PHE>
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In-Reply-To: <00b001c276ba$1533dbf0$3500080a@PHE>; from pete@he.iki.fi on Fri, Oct 18, 2002 at 06:21:37PM +0300
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On Fri, Oct 18, 2002 at 06:21:37PM +0300, Petri Helenius wrote:
...
> Luigi´s polling work would be useful here. That would lead to incorrect
> timestamps
> on the packets, though?

polling introduce an extra uncertainty which might be as large as
an entire clock tick, yes.

But even with interrupts, you cannot trust the time when the interrupt
driver is run -- there are cases where an ISR is delayed by 10ms or more.
And even when it runs, it might take quite a bit of time (up to a
few 100's of microseconds) to drain the receive queue from packets
received earlier.

in normal cases, timestamps are reasonably accurate in both cases.
In special cases, the error induced by having interrupts blocked
causes errors which are much larger than polling alone.

	cheers
	luigi

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