selftests/powerpc: Fix generation of vector instructions/types in context_switch

Currently it doesn't appear the resulting binary actually uses any
Altivec or VSX instructions the solution is to explicitly tell GCC to
use vector instructions and use vector types in the code.

Part of this this issue can be GCC version specific:

GCC 4.9.x is happy to use Altivec and VSX instructions if altivec.h is
includedi (and possibly if vector types are used), this also means that
4.9.x will use VSX instructions even if only -maltivec is passed. It is
also possible that Altivec instructions will be used even without
-maltivec or -mabi=altivec.

GCC 5.2.x complains about the lack of -maltivec parameter if altivec.h
is included and will not use VSX unless -mvsx is present on commandline.

GCC 5.3.0 has a regression that means __attribute__((__target__("no-vsx"))
fails to build. A fix is targeted for 5.4.

Furthermore LTO (Link Time Optimisation) doesn't play well with
__attribute__((__target__("no-vsx")), LTO can cause GCC to forget about
the attribute and compile with VSX instructions regardless. Be wary when
enabling -flfo for this test.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/tools/testing/selftests/powerpc/benchmarks/Makefile b/tools/testing/selftests/powerpc/benchmarks/Makefile
index 912445ff7ce76637619d4a8e47beae59b3678001..6816fc2140cb318a002e9a8138701664dbc7e65d 100644 (file)
--- a/tools/testing/selftests/powerpc/benchmarks/Makefile
+++ b/tools/testing/selftests/powerpc/benchmarks/Makefile
@@ -7,6 +7,7 @@ all: $(TEST_PROGS)
 $(TEST_PROGS): ../harness.c
 
 context_switch: ../utils.c
+context_switch: CFLAGS += -maltivec -mvsx -mabi=altivec
 context_switch: LDLIBS += -lpthread
 
 include ../../lib.mk

diff --git a/tools/testing/selftests/powerpc/benchmarks/context_switch.c b/tools/testing/selftests/powerpc/benchmarks/context_switch.c
index e6af382a305a09a64791682b7af51e9a0b2097b4..a36883ad48a451799f3345e048e6e1f5d52ed33e 100644 (file)
--- a/tools/testing/selftests/powerpc/benchmarks/context_switch.c
+++ b/tools/testing/selftests/powerpc/benchmarks/context_switch.c
@@ -25,7 +25,9 @@
 #include <sys/types.h>
 #include <sys/shm.h>
 #include <linux/futex.h>
-
+#ifdef __powerpc__
+#include <altivec.h>
+#endif
 #include "../utils.h"
 
 static unsigned int timeout = 30;
@@ -37,12 +39,15 @@ static int touch_fp = 1;
 double fp;
 
 static int touch_vector = 1;
-typedef int v4si __attribute__ ((vector_size (16)));
-v4si a, b, c;
+vector int a, b, c;
 
 #ifdef __powerpc__
 static int touch_altivec = 1;
 
+/*
+ * Note: LTO (Link Time Optimisation) doesn't play well with this function
+ * attribute. Be very careful enabling LTO for this test.
+ */
 static void __attribute__((__target__("no-vsx"))) altivec_touch_fn(void)
 {
        c = a + b;