Date: Thu, 17 Sep 1998 11:08:56 +0200 (SAT) From: John Hay <jhay@mikom.csir.co.za> To: phk@critter.freebsd.dk (Poul-Henning Kamp) Cc: mike@smith.net.au, current@FreeBSD.ORG, bde@FreeBSD.ORG Subject: Re: Death by SIGXCPU (problems with our clock code) Message-ID: <199809170908.LAA06018@zibbi.mikom.csir.co.za> In-Reply-To: <8620.906017842@critter.freebsd.dk> from Poul-Henning Kamp at "Sep 17, 98 09:37:22 am"
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So, do you have better test code that is available, or should I just use
Mike's? I would really also like to find out what the problem is, because
I have just about given up trying to get PPS working properly from sio
interrupts on 486 and SMP machines. On my two machines that use the 8254
for the timecounter I see forward jumps.
John
--
John Hay -- John.Hay@mikom.csir.co.za
>
> Mike,
>
> >Since nobody else has taken up my suggestion to instrument the code to
> >find out what's going on, I've shouldered the cross.
>
> I have my version here instrumented far more than what you've done,
> and I have two and a half extra kinds of timecounting hardware
> running here in my lab but I have not been able to catch it in
> flagrante delico yet, leading me to conclude that some hardware is
> involved.
>
> The check in microtime and nanotime are strictly not valid. The
> reason is that both microtime and nanotime are reentrant now, so
> you might take an interrupt in the middle of it.
>
> The reentrancy could possibly be a problem if some spl*() are missing
> somewhere else, or if logic is flawed in the code. You can test
> that hypothesis by splalot() around the [get]{micro|nano}[run]time()
> functions.
>
> I am puzzeled about the negative fractions and I think they are the
> most important clue.
>
> tco_forward() does not do any sanity checks on the timecounter, so
> if there is some trouble with the hardware (or our method of
> accessing it), that would shine straight through.
>
> Can you please add a check to the i8254/tsc get_timecount functions
> (in isa/clock.c) which report if the count goes backwards or is
> bigger than (1/HZ + epsilon) seconds ?
>
> What machine is this on ?
>
> What is your timecounter TSC/i8254 ?
>
> BIOS settings ?
>
> Bruce: You mentioned that some i8254 cloneoids didn't implement
> the latch correctly any references to that ?
>
> Poul-Henning
>
> --
> 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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