Messages in this thread | | | Date | Fri, 7 Nov 2008 13:14:12 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC patch 04/18] get_cycles() : powerpc64 HAVE_GET_CYCLES |
| |
* Josh Boyer (jwboyer@linux.vnet.ibm.com) 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@polymtl.ca> > >CC: benh@kernel.crashing.org > >CC: paulus@samba.org > >CC: David Miller <davem@davemloft.net> > >CC: Linus Torvalds <torvalds@linux-foundation.org> > >CC: Andrew Morton <akpm@linux-foundation.org> > >CC: Ingo Molnar <mingo@redhat.com> > >CC: Peter Zijlstra <a.p.zijlstra@chello.nl> > >CC: Thomas Gleixner <tglx@linutronix.de> > >CC: Steven Rostedt <rostedt@goodmis.org> > >CC: linux-arch@vger.kernel.org > >--- > > 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
| |