* Josh Boyer (jwboyer@xxxxxxxxxxxxxxxxxx) wrote:
> On Fri, Nov 07, 2008 at 12:23:40AM -0500, Mathieu Desnoyers wrote:
> >This patch selects HAVE_GET_CYCLES and makes sure get_cycles_barrier() and
> >get_cycles_rate() are implemented.
> >
> >Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> >CC: benh@xxxxxxxxxxxxxxxxxxx
> >CC: paulus@xxxxxxxxx
> >CC: David Miller <davem@xxxxxxxxxxxxx>
> >CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> >CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >CC: Ingo Molnar <mingo@xxxxxxxxxx>
> >CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> >CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
> >CC: linux-arch@xxxxxxxxxxxxxxx
> >---
> > arch/powerpc/Kconfig | 1 +
> > arch/powerpc/include/asm/timex.h | 11 +++++++++++
> > 2 files changed, 12 insertions(+)
> >
> >Index: linux.trees.git/arch/powerpc/Kconfig
> >===================================================================
> >--- linux.trees.git.orig/arch/powerpc/Kconfig 2008-11-07 00:09:44.000000000 -0500
> >+++ linux.trees.git/arch/powerpc/Kconfig 2008-11-07 00:09:46.000000000 -0500
> >@@ -121,6 +121,7 @@ config PPC
> > select HAVE_DMA_ATTRS if PPC64
> > select USE_GENERIC_SMP_HELPERS if SMP
> > select HAVE_OPROFILE
> >+ select HAVE_GET_CYCLES if PPC64
>
> So maybe it's just me because it's Friday and I'm on vacation, but I don't
> see anything overly specific to ppc64 here. In fact, you use get_cycles_rate
> for all of powerpc in a later patch in the series.
>
> Is there something special about HAVE_GET_CYCLES that I'm missing that would
> make it only apply to ppc64 and not ppc32?
>
> josh
Hi Josh,
powerpc32 only uses the 32 LSBs for the TSC in the current get_cycles()
implementation. We could either define HAVE_GET_CYCLES_32 like I did on
mips32, or change get_cycles so it also reads the 32 MSBs in a loop like
this (it does not take care of the CPU_FTR_CELL_TB_BUG though) :
typedef unsigned long long cycles_t;
cycles_t get_cycles_ppc32(void)
{
union {
cycles_t v;
struct {
u32 ms32, ls32; /* powerpc is big endian */
} s;
} cycles;
do {
cycles.ls32 = mftbu();
cycles.ms32 = mftbl();
} while (cycles.ls32 != mftbu());
return cycles.v;
}
I'd prefer this second solution. If one needs a specific get_cycles() to
be only 32-bits (but really really fast) for the scheduler, then this
could be a get_cycles_sched() or something like this which does not
guarantee that it returns full 64-bits...
Mathieu
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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