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Date: Fri, 5 Feb 1999 21:15:57 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199902051015.VAA01285@godzilla.zeta.org.au>
To: adam@veda.is, mike@smith.net.au
Subject: Re: cvs commit: src/sys/i386/conf GENERIC
Cc: adam@FreeBSD.ORG, cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG,
        nate@mt.sri.com, phk@critter.freebsd.dk
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>> > This should be backed out, the correct fix for these systems is to
>> > 
>> > 	sysctl -w kern.timecounter.method=1

This seems backwards.  How can a fix for too-small h/w timecounter
wraparound time affect systems using the TSC for a timecounter?
The wraparound time for a 500MHz TSC is a measly 1169 years.

I don't understand how the fix helps for i8254 timecounters either
-- clkintr() in effect reads the i8254, and if clkintr() doesn't get
called often enough (every 2/hz - delta) seconds, then there isn't much
chance of extra i8254 reads due to method=1.  Perhaps there are just a
few critical i8254 reads after apm wakes things up (internal state of
i8254_get_timecount() is hosed at wakeup time but it may get fixed as
a side effect of method=1).

>> Fair enough, but it should be documented somewhere obvious (i.e. as an
>> agreeable comment in GENERIC) to keep POLA. I certainly didn't expect the
>> removal of apm to mess up the timecounter.

>The code in question can actually detect the need for this sysctl 
>adjustment.  I again request that it make it as required.

How can it do that?  I can't detect any need for this sysctl :-).

Bruce

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