cvs commit: src/sys/conf options.i386 src/sys/i386/i386 tsc.c src/sys/i386/conf NOTES

[Poul-Henning Kamp]

In message <xzpof3js45j.fsf at flood.ping.uio.no>, Dag-Erling Smorgrav writes:
>--=-=-=
>
>Nate Lawson <nate at 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 at 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.