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Date:      Thu, 17 May 2001 10:11:47 +0200
From:      Poul-Henning Kamp <phk@critter.freebsd.dk>
To:        Mike Smith <msmith@FreeBSD.ORG>
Cc:        Bruce Evans <bde@zeta.org.au>, freebsd-questions@FreeBSD.ORG, arch@FreeBSD.ORG
Subject:   Re: Gettimeofday Again... 
Message-ID:  <10771.990087107@critter>
In-Reply-To: Your message of "Thu, 17 May 2001 01:13:43 PDT." <200105170813.f4H8DhE01424@mass.dis.org> 

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In message <200105170813.f4H8DhE01424@mass.dis.org>, Mike Smith writes:
>> >     I don't change the timercounter method defaults, and I sure hope you
>> >     aren't advocating that people change their timecounter defaults.  If
>> >     the TSC is a reasonable default, the system should figure it out and
>> >     use it without requiring intervention.
>> 
>> It's only a reasonable default if apm (or possibly acpica) is configured
>> (and used).
>
>The TSC is never a reasonable default; there is no good way to be certain 
>that the TSC is and/or will remain stable.  Even with ACPI, you can't be 
>entirely sure.

Right.  I have tried some hybrid schemes where the TSC is interpolating
between i8254 interrupts, but it is all but impossible to maintain
continuity on a clock-throttling laptop...

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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