Actually, I was wrong, the mpc8379 is an e300c4.

So it seems clear to me that we compile in the book3s code because
this is an 83xx CPU part.  I also see that Kconfig knows that I have
an core-fsl-emb but we don't actually compile the PMU backend for it
because there's no support for anything but e500.

mort@chinook:~/src/s4v2-glibc/linux-mpc$ grep PERF .config
CONFIG_FSL_EMB_PERFMON=y
CONFIG_PPC_PERF_CTRS=y
CONFIG_HAVE_PERF_EVENTS=y
CONFIG_PERF_EVENTS=y
# CONFIG_DEBUG_PERF_USE_VMALLOC is not set
mort@chinook:~/src/s4v2-glibc/linux-mpc$ grep BOOK3S .config
CONFIG_PPC_BOOK3S_32=y
CONFIG_PPC_BOOK3S=y

more below...

On Tue, Oct 15, 2013 at 4:39 PM, Benjamin Herrenschmidt
[off-list ref] wrote:

quoted

On Tue, 2013-10-15 at 15:22 -0500, Scott Wood wrote:

quoted

On Tue, 2013-10-15 at 14:53 -0500, Benjamin Herrenschmidt wrote:

quoted

On Tue, 2013-10-15 at 14:44 -0400, Martin Hicks wrote:

quoted

quoted

This is an e300 core right ? (603...). Do that have an SIAR at all
(Scott ?)

Yes, e300c3.

Ok so I have a hard time figuring out how that patch can make a
difference since for all I can see, there is no perf backend upstream
for e300 at all :-(

I must certainly be missing something ... Scott, can you have a look ?

e300c3 has a core-fsl-emb style performance monitor (though Linux
doesn't support it yet).  If a bug was bisected to a change in
core-book3s.c, then it's probably a coincidence due to moving code
around.

CONFIG_PPC_PERF_CTRS seems to give the mpc8379 some kind of basic
performance measuring.  Is this through dummy_perf() in
arch/powerpc/kernel/pmc.c?

quoted

Mort, can you see if just that change is enough to cause the problem ?

It is not.  The patch that does get IPs working again in my 3.11 tree
is this one:

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index eeae308..9a3f572 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c

@@ -122,10 +122,6 @@ void power_pmu_flush_branch_stack(void) {}
 static inline void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw) {}
 #endif /* CONFIG_PPC32 */

-static bool regs_use_siar(struct pt_regs *regs)
-{
-       return !!regs->result;
-}

 /*
  * Things that are specific to 64-bit implementations.

@@ -1802,14 +1798,13 @@ unsigned long perf_misc_flags(struct pt_regs *regs)
  */
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
 {
-       bool use_siar = regs_use_siar(regs);
-
-       if (use_siar && siar_valid(regs))
-               return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
-       else if (use_siar)
-               return 0;               // no valid instruction pointer
-       else
+       unsigned long mmcra = regs->dsisr;
+       if (TRAP(regs) != 0xf00)
+               return regs->nip;
+       if ((ppmu->flags & PPMU_NO_CONT_SAMPLING) &&
+           !(mmcra & MMCRA_SAMPLE_ENABLE))
                return regs->nip;
+       return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
 }

 static bool pmc_overflow_power7(unsigned long val)

mh