On Thursday 24 November 2005 21:36, Bernd Paysan wrote:
That's the only board I've ever seen in years where I can't use PIT/TSC (on four out of seven!). There are several other Linux PCs in the office, and two at home, and all work fine with PIT/TSC, except the dual-Opteron system (running SuSE 9.3), which needs the HPET timer, since the TSC based timekeeping doesn't work with different CPUs having different speeds.
After a bit more investigation, it turned out that it is indeed the TSC-problem with dual cores. Setting the option "clock=pmtmr notsc" is mandatory on a dual-core Athlon, despite the TSC desynchronization is very small over time. What I don't understand is why there is any TSC desynchronization at all. The two cores run at the same frequency all the time, anyway (you can't set one to 1GHz and the other to 2GHz via Cool'n'Quiet). That's why the problem doesn't show up for a while, and some random component is necessary to see the full effect. Conclusion: You can't rely on the TSC if you have more than one CPU, and a power-saving policy in effect. It would be better to switch the stuff off automatically in that case - until AMD and Intel deliver CPUs with synchronized TSCs next year. Or to resynchronize the TSCs after each frequency change (using the PIT or PM timer as reference then). -- Bernd Paysan "If you want it done right, you have to do it yourself" http://www.jwdt.com/~paysan/