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Subject: Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 tsc.c
 src/sys/i386/conf NOTES
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> Tor Egge <tegge@FreeBSD.org> writes:
> >   Log:
> >   Add SMP_TSC option, which can be used on SMP systems where the TSCs
> >   are synchronized to reduce context switch cost.
> 
> Out of curiosity, what kind of systems would that be?

Dell PowerEdge 2450, 2 x 733 MHz PIII CPUs, 1 GB memory.

Elapsed times of "dd if=/dev/da0s4g of=/dev/null bs=512 count=200000" test:

5.0-CURRENT	5.0-CURRENT	5.0-CURRENT	4.8-RELEASE	4.8-RELEASE
i8254		ACPI-safe	TSC		i8254		TSC
48.010578	35.460545	29.709355	13.326655	12.426712
48.041532	35.153883	29.797299	13.359450	12.411480
48.039143	35.113667	29.610601	13.349306	12.804534
47.630433	35.163372	30.036985	13.258281	12.473128
47.693183	35.240809	29.728361	13.332692	12.473128

Which gives average microseconds/read of

239		176		149		67		63

- Tor Egge