selftests/powerpc: Count instructions under scheduler pressure

Have a task eat some cpu while we are counting instructions to create
some scheduler pressure. The idea being to try and unearth any bugs we
have in counting that only appear when context switching is happening.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

tools/testing/selftests/powerpc/pmu/Makefile

@@ -2,7 +2,7 @@ noarg:
 	$(MAKE) -C ../
 
 PROGS := count_instructions l3_bank_test
-EXTRA_SOURCES := ../harness.c event.c
+EXTRA_SOURCES := ../harness.c event.c lib.c
 
 SUB_TARGETS = ebb
 

tools/testing/selftests/powerpc/pmu/count_instructions.c

@@ -12,6 +12,7 @@
 
 #include "event.h"
 #include "utils.h"
+#include "lib.h"
 
 extern void thirty_two_instruction_loop(u64 loops);
 
@@ -90,7 +91,7 @@ static u64 determine_overhead(struct event *events)
 	return overhead;
 }
 
-static int count_instructions(void)
+static int test_body(void)
 {
 	struct event events[2];
 	u64 overhead;
@@ -129,6 +130,11 @@ static int count_instructions(void)
 	return 0;
 }
 
+static int count_instructions(void)
+{
+	return eat_cpu(test_body);
+}
+
 int main(void)
 {
 	return test_harness(count_instructions, "count_instructions");