cvs commit: src/sys/amd64/amd64 cpu_switch.S machdep.c

David O'Brien obrien at
Tue Oct 18 07:41:07 PDT 2005

On Tue, Oct 18, 2005 at 09:44:02AM -0400, Andrew Gallatin wrote:
> It is a shame we can't find a way to use the TSC as a timecounter on
> SMP systems.  It seems that about 40% of the context switch time is
> spent just waiting for the PIO read of the ACPI-fast or i8254 to
> return.

Revision F Opterion's will have the RDTSCP (read serialized TSC pair)
instruction that helps some.  Slide 13 of 

Future Opteron's (or what ever AMD will call it then) will have a P-state
invarient TSC in 2007.

-- David  (obrien at

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