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To: Dag-Erling Smorgrav <des@ofug.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sun, 06 Apr 2003 23:32:40 +0200."
             <xzpof3js45j.fsf@flood.ping.uio.no> 
Date: Mon, 07 Apr 2003 00:03:59 +0200
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cc: Tor.Egge@cvsup.no.freebsd.org
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cc: Nate Lawson <nate@root.org>
Subject: Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 tsc.c
	src/sys/i386/conf NOTES 
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In message <xzpof3js45j.fsf@flood.ping.uio.no>, Dag-Erling Smorgrav writes:
>--=-=-=
>
>Nate Lawson <nate@root.org> writes:
>> Perhaps you could enable this option by default if it had a corresponding
>> check for drift that would disable it if things got out of hand.
>
>There wouldn't be much point in that unless the SMP_TSC option also
>forced the TSC to be selected at boot time.  On most SMP systems, the
>PIIX timecounter is automatically selected by virtue of being
>discovered last.

It is specifically discovered last because it should be used if
at all possible.

>I must have bad benchmark karma, BTW - I can see no reduction of
>context switch time or any other significant performance boost when
>using the TSC on my dual Celeron system.

There is a big difference if you get to use "ACPI-fast" (correctly
implemented hardware) instead of "ACPI-safe" (buggy hardware).

-- 
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.