RE: test_stack on powerpc (power7)

On Wed, 2014-01-29 at 07:05 +0000, Boehm, Hans wrote:
> Interesting.
<...snip...>

> I would also check that the recheck of first against AO_load(list) appears in the assembly code where it should.

Thanks for the suggestions. :-)

I looked closer at the code that does the x_bits twiddling, and after a
bit of quality time single-stepping within gdb, have found an issue.
The AO_load() function is being mapped to AO_load() in
sysdeps/loadstore/atomic_load.h, rather than the AO_load_acquire() in
powerpc.h like I had initialy thought, per the #defines I was lookging
at in generalize-small.h.  The critical detail in that is the lack of an
isync in the atomic_load.h version.

I'm admittedly unclear of how the path through the header file includes
should be.

The patch below (inline and attached) seems a bit hackish to me, but is
also sufficient to allow test_stack to run to completion on the P7 here.
(test_stack running in a loop, ~ 1000 successful runs so far).   For
inclusion as-is, or as inspiration to whomever better understands the
include hierarchy.

Thanks, 
-Will

--

Force AO_load() to map to AO_load_acquire() for powerpc.  The
AO_load_acquire() function includes isync instructions that
are critical for proper behavior on power system.


Signed-Off-By: Will Schmidt <will_schmidt-DhXWPJtHtuFWk0Htik3J/[email protected]>


diff -aur --exclude='*.Plo' --exclude='*.Po' libatomic_ops-7.4.0/src/atomic_ops/sysdeps/gcc/powerpc.h libatomic_ops-7.4.0.new/src/atomic_ops/sysdeps/gcc/powerpc.h
--- libatomic_ops-7.4.0/src/atomic_ops/sysdeps/gcc/powerpc.h	2013-11-10 03:57:17.000000000 -0600
+++ libatomic_ops-7.4.0.new/src/atomic_ops/sysdeps/gcc/powerpc.h	2014-01-30 12:17:20.819984940 -0600
@@ -29,6 +29,8 @@
 
 #include "../all_aligned_atomic_load_store.h"
 
+#define AO_load(addr) AO_load_acquire(addr)
+
 #include "../test_and_set_t_is_ao_t.h"
         /* There seems to be no byte equivalent of lwarx, so this       */
         /* may really be what we want, at least in the 32-bit case.     */

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diff -aur --exclude='*.Plo' --exclude='*.Po' libatomic_ops-7.4.0/src/atomic_ops/sysdeps/gcc/powerpc.h libatomic_ops-7.4.0.new/src/atomic_ops/sysdeps/gcc/powerpc.h
--- libatomic_ops-7.4.0/src/atomic_ops/sysdeps/gcc/powerpc.h	2013-11-10 03:57:17.000000000 -0600
+++ libatomic_ops-7.4.0.new/src/atomic_ops/sysdeps/gcc/powerpc.h	2014-01-30 12:17:20.819984940 -0600
@@ -29,6 +29,8 @@
 
 #include "../all_aligned_atomic_load_store.h"
 
+#define AO_load(addr) AO_load_acquire(addr)
+
 #include "../test_and_set_t_is_ao_t.h"
         /* There seems to be no byte equivalent of lwarx, so this       */
         /* may really be what we want, at least in the 32-bit case.     */