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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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