Date: Mon, 30 Nov 1998 14:51:59 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Mike Smith <mike@smith.net.au> Cc: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern kern_clock.c Message-ID: <12028.912433919@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 30 Nov 1998 05:38:52 PST." <199811301338.FAA03590@dingo.cdrom.com>
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In message <199811301338.FAA03590@dingo.cdrom.com>, Mike Smith writes:
>> phk 1998/11/29 12:31:03 PST
>>
>> Modified files:
>> sys/kern kern_clock.c
>> Log:
>> Make the previous behaviour the default, add a sysctl which you
>> can set if your hw/sw produces the "calcru negative..." message.
>
>The sysctl should be automatically set by the "calcru negative ..."
>detection code.
No, because at that time you clock has already been warped out of
shape. People need to know and be aware that their sw/hw has a problem.
>> Setting the alternate method (sysctl -w kern.timecounter.method=1)
>> makes the the get{nano|micro}*() functions call the real thing at
>> resulting in a measurable but minor overhead.
>
>This smells like a botch, not a fix.
No, it isn't. get{nano|micro}* are supposed to be precise to within
a tick, for things where better precision is pointless and where
speed is important. After I changed the method to the one which is
now known as "1", it became imprecise to within one second, and that
broke various stuff.
>> I decided to NOT have the "calcru" change the method automatically
>> because you should be aware of this problem if you have it.
>
>Bad. There is now no correspondence between the diagnostic and the
>fix, and the user has to vector through a small number of people in
>order to resolve their problems.
I submitted a FAQ entry.
--
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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