On Tue, Jun 02, 2015 at 12:41:27PM -0700, Andy Lutomirski wrote: > On Tue, Jun 2, 2015 at 12:33 PM, Thomas Gleixner <t...@linutronix.de> wrote: > > On Thu, 21 May 2015, Adrian Hunter wrote: > > > >> If it takes longer than 12us to read the PIT counter lsb/msb, > >> then the error margin will never fall below 500ppm within 50ms, > >> and Fast TSC calibration will always fail. > > > > So finally the legacy PIT emulation takes longer than the 30 years old > > hardware implementation. Progress! > > > >> This patch detects when that will happen and switches to using > >> a slightly different algorithm that takes advantage of the PIT's > >> latch comand. > > > > Is there really no smarter way to figure out the TSC frequency on > > modern systems? > > I just asked Len this question yesterday. intel_pstate can do it, > although the algorithm is a bit gross.
intel_pstate needs to know the model number. If you know the model number sure you can do a lot better (e.g. using the ref-clock fixed counter or some other methods) But if you don't you need something else. And at some point the only thing left over is the PIT. -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
