From owner-freebsd-hackers Tue Feb 5 8:36: 5 2002
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Date: Tue, 05 Feb 2002 09:35:35 -0700 (MST)
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To: phk@critter.freebsd.dk
Cc: jdp@polstra.com, hackers@FreeBSD.ORG, msmith@hub.freebsd.org
Subject: Re: A question about timecounters
From: "M. Warner Losh" <imp@village.org>
In-Reply-To: <86051.1012909502@critter.freebsd.dk>
References: <200202050141.g151fxW02520@vashon.polstra.com>
<86051.1012909502@critter.freebsd.dk>
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In message: <86051.1012909502@critter.freebsd.dk>
Poul-Henning Kamp <phk@critter.freebsd.dk> writes:
: But the i8254 is a piece of shit in this context, and due to
: circumstances (apm being enabled0 most machines end up using the
: i8254 by default.
:
: My (and I belive Bruce's) diagnosis so far is that most problems
: come from the i8254 timecounter.
We measured pps interrupts with the i8254 timecounter in a fast
interrupt handler via the parallel port (yes, we hacked it to give us
a fast interrupt). We found lots of outliers on the order of a few
milliseconds in the data that we had to discard because they were
obviously bogus. We don't know if this is because of interrupt
latency or because of bugs in the 8254 timecounter code/hardware. At
the time, it wasn't important enough to do a detailed numerology on to
see if more data couldn't be mined from it or not. And the data that
we saw the outliers in was somewhat processed from the original
data...
Warner
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