Is the TSC timecounter safe on SMP system?
dwhite at gumbysoft.com
Fri Aug 13 10:38:30 PDT 2004
On Fri, 13 Aug 2004, Andrew Gallatin wrote:
> I have a system where the TSC timecounter is quite a bit more accurate
> (or perhaps its just much cheaper) than the ACPI timecounter. This is a
> single CPU, HTT system running an SMP kernel.
> A simple program which calls gettimeofday() in a tight loop, looking
> for the microseconds to change sees ~998,000 microsecond updates/sec
> with kern.timecounter.hardware=TSC, and 28,500 updates/sec with ACPI-safe.
> 1) Is it safe to switch to TSC?
If you like your ticks bouncing around; you'll get different values
depending on which CPU you read.
> 2) If yes, would it be safe to switch to TSC if this was a real
> SMP system with multiple physical cpus?
TSC in a single-package HTT situation would be interesting to research, if
it is shared across the pipelines.
Doug White | FreeBSD: The Power to Serve
dwhite at gumbysoft.com | www.FreeBSD.org
More information about the freebsd-current