On Thu, Oct 16, 2008 at 07:27:34PM -0400, Mathieu Desnoyers wrote: > partly reverts commit efb9ca08b5a2374b29938cdcab417ce4feb14b54. Selects > HAVE_GET_CYCLES_32 only on CPUs where it is safe to use it. > > Currently consider the "_WORKAROUND" cases for 4000 and 4400 to be unsafe, but > should probably add other sub-architecture to the blacklist. > > Do not define HAVE_GET_CYCLES because MIPS does not provide 64-bit tsc (only > 32-bits). [...] > Index: linux-2.6-lttng/include/asm-mips/timex.h > =================================================================== > --- linux-2.6-lttng.orig/include/asm-mips/timex.h 2008-10-16 12:25:47.000000000 -0400 > +++ linux-2.6-lttng/include/asm-mips/timex.h 2008-10-16 12:34:18.000000000 -0400 > @@ -29,14 +29,39 @@ > * which isn't an evil thing. > * > * We know that all SMP capable CPUs have cycle counters. > + * > + * Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> > + * HAVE_GET_CYCLES makes sure that this case is handled properly : > + * > + * Ralf Baechle <ralf@xxxxxxxxxxxxxx> : > + * This avoids us executing an mfc0 c0_count instruction on processors which > + * don't have but also on certain R4000 and R4400 versions where reading from > + * the count register just in the very moment when its value equals c0_compare > + * will result in the timer interrupt getting lost. > */ The usual workaround for this processor bug is to check if the value of the c0_count and c0_compare registers are close. Clone, not identical to allow for the time skew in the pipeline. If they are close, then execute the timer interrupt handler. See also the R4000/R4400 errata. Ralf -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
