ARM: kprobes: Add some benchmarking to test module

These benchmarks show the basic speed of kprobes and verify the success
of optimisations done to the emulation of typical function entry
instructions (i.e. push/stmdb).
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

arch/arm/kernel/kprobes-test.c

@@ -185,6 +185,9 @@
 #include "kprobes-test.h"
 
 
+#define BENCHMARKING	1
+
+
 /*
  * Test basic API
  */
@@ -443,6 +446,157 @@ static int run_api_tests(long (*func)(long, long))
 }
 
 
+/*
+ * Benchmarking
+ */
+
+#if BENCHMARKING
+
+static void __naked benchmark_nop(void)
+{
+	__asm__ __volatile__ (
+		"nop		\n\t"
+		"bx	lr"
+	);
+}
+
+#ifdef CONFIG_THUMB2_KERNEL
+#define wide ".w"
+#else
+#define wide
+#endif
+
+static void __naked benchmark_pushpop1(void)
+{
+	__asm__ __volatile__ (
+		"stmdb"wide"	sp!, {r3-r11,lr}  \n\t"
+		"ldmia"wide"	sp!, {r3-r11,pc}"
+	);
+}
+
+static void __naked benchmark_pushpop2(void)
+{
+	__asm__ __volatile__ (
+		"stmdb"wide"	sp!, {r0-r8,lr}  \n\t"
+		"ldmia"wide"	sp!, {r0-r8,pc}"
+	);
+}
+
+static void __naked benchmark_pushpop3(void)
+{
+	__asm__ __volatile__ (
+		"stmdb"wide"	sp!, {r4,lr}  \n\t"
+		"ldmia"wide"	sp!, {r4,pc}"
+	);
+}
+
+static void __naked benchmark_pushpop4(void)
+{
+	__asm__ __volatile__ (
+		"stmdb"wide"	sp!, {r0,lr}  \n\t"
+		"ldmia"wide"	sp!, {r0,pc}"
+	);
+}
+
+
+#ifdef CONFIG_THUMB2_KERNEL
+
+static void __naked benchmark_pushpop_thumb(void)
+{
+	__asm__ __volatile__ (
+		"push.n	{r0-r7,lr}  \n\t"
+		"pop.n	{r0-r7,pc}"
+	);
+}
+
+#endif
+
+static int __kprobes
+benchmark_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	return 0;
+}
+
+static int benchmark(void(*fn)(void))
+{
+	unsigned n, i, t, t0;
+
+	for (n = 1000; ; n *= 2) {
+		t0 = sched_clock();
+		for (i = n; i > 0; --i)
+			fn();
+		t = sched_clock() - t0;
+		if (t >= 250000000)
+			break; /* Stop once we took more than 0.25 seconds */
+	}
+	return t / n; /* Time for one iteration in nanoseconds */
+};
+
+static int kprobe_benchmark(void(*fn)(void), unsigned offset)
+{
+	struct kprobe k = {
+		.addr		= (kprobe_opcode_t *)((uintptr_t)fn + offset),
+		.pre_handler	= benchmark_pre_handler,
+	};
+
+	int ret = register_kprobe(&k);
+	if (ret < 0) {
+		pr_err("FAIL: register_kprobe failed with %d\n", ret);
+		return ret;
+	}
+
+	ret = benchmark(fn);
+
+	unregister_kprobe(&k);
+	return ret;
+};
+
+struct benchmarks {
+	void		(*fn)(void);
+	unsigned	offset;
+	const char	*title;
+};
+
+static int run_benchmarks(void)
+{
+	int ret;
+	struct benchmarks list[] = {
+		{&benchmark_nop, 0, "nop"},
+		/*
+		 * benchmark_pushpop{1,3} will have the optimised
+		 * instruction emulation, whilst benchmark_pushpop{2,4} will
+		 * be the equivalent unoptimised instructions.
+		 */
+		{&benchmark_pushpop1, 0, "stmdb	sp!, {r3-r11,lr}"},
+		{&benchmark_pushpop1, 4, "ldmia	sp!, {r3-r11,pc}"},
+		{&benchmark_pushpop2, 0, "stmdb	sp!, {r0-r8,lr}"},
+		{&benchmark_pushpop2, 4, "ldmia	sp!, {r0-r8,pc}"},
+		{&benchmark_pushpop3, 0, "stmdb	sp!, {r4,lr}"},
+		{&benchmark_pushpop3, 4, "ldmia	sp!, {r4,pc}"},
+		{&benchmark_pushpop4, 0, "stmdb	sp!, {r0,lr}"},
+		{&benchmark_pushpop4, 4, "ldmia	sp!, {r0,pc}"},
+#ifdef CONFIG_THUMB2_KERNEL
+		{&benchmark_pushpop_thumb, 0, "push.n	{r0-r7,lr}"},
+		{&benchmark_pushpop_thumb, 2, "pop.n	{r0-r7,pc}"},
+#endif
+		{0}
+	};
+
+	struct benchmarks *b;
+	for (b = list; b->fn; ++b) {
+		ret = kprobe_benchmark(b->fn, b->offset);
+		if (ret < 0)
+			return ret;
+		pr_info("    %dns for kprobe %s\n", ret, b->title);
+	}
+
+	pr_info("\n");
+	return 0;
+}
+
+#endif /* BENCHMARKING */
+
+
 /*
  * Decoding table self-consistency tests
  */
@@ -1526,6 +1680,13 @@ static int __init run_all_tests(void)
 		goto out;
 	}
 
+#if BENCHMARKING
+	pr_info("Benchmarks\n");
+	ret = run_benchmarks();
+	if (ret)
+		goto out;
+#endif
+
 #if __LINUX_ARM_ARCH__ >= 7
 	/* We are able to run all test cases so coverage should be complete */
 	if (coverage_fail) {