John Baldwin writes: > On Friday 13 August 2004 12:49 pm, 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? > > > > 2) If yes, would it be safe to switch to TSC if this was a real > > SMP system with multiple physical cpus? > > Probably not. The problem is that the TSC is not necessarily in sync between > the CPUs so time would "jump around" as you migrated between CPUs. If you > can get the TSC's synchronized between the CPUs and keep them that way then > you can use the TSC (Linux does this FWIW). > But on a single CPU HTT machine, does each HTT core reads the same TSC? DrewReceived on Fri Aug 13 2004 - 15:28:57 UTC
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