Date: Sun, 08 Nov 1998 11:10:07 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Bruce Evans <bde@zeta.org.au> Cc: current@FreeBSD.ORG, wpaul@skynet.ctr.columbia.edu Subject: Re: Grrr... calcru: negative time blah blah blah Message-ID: <14665.910519807@critter.freebsd.dk> In-Reply-To: Your message of "Sun, 08 Nov 1998 21:05:41 %2B1100." <199811081005.VAA24481@godzilla.zeta.org.au>
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In message <199811081005.VAA24481@godzilla.zeta.org.au>, Bruce Evans writes:
>>>Timecounter strangeness seems to be only a symptom here. I've seen
>>>similar strangeness caused by ddb masking interrupts. However,
>>>{micro|nano}[run]time() only have obvious problems when tco_delta()
>>>overflows a u_int. Overflow occurs after only about 10 seconds for
>>>a 400MHz tsc timecounter, but not for one hour for an i8254 timecounter.
>>
>>Uhm, it happens earlier for a i8254, in fact it happens whenever more
>>than one interrupt is lost. The majority of the bits are software
>>bits.
>
>That's neither (C) overflow nor in {micro|nano}[run]time(). When the
>low-level i8254 timecounter is not called often enough, the timecounter
>just drops some multiple of timer0_max_count (about 11932) timecounter
>ticks. This doesn't necessarily happen when more than one interrupt
>is lost -- it happens when the low-level timecounter is not called for
>more than (2 - epsilon) interrupt periods. There must have been some
>low-level timecounter calls for the observed timecounter deltas to be
>more than (2 * timer0_max_count).
ahh, DuH!, yes. erhm. you're right...
So we're back to square one: this doesn't really look like a
timecounter problem...
--
Poul-Henning Kamp FreeBSD coreteam member
phk@FreeBSD.ORG "Real hackers run -current on their laptop."
"ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal
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