selftests/bpf: Add uprobe triggering overhead benchmarks

Add benchmark to measure overhead of uprobes and uretprobes. Also have
a baseline (no uprobe attached) benchmark.

On my dev machine, baseline benchmark can trigger 130M user_target()
invocations. When uprobe is attached, this falls to just 700K. With
uretprobe, we get down to 520K:

  $ sudo ./bench trig-uprobe-base -a
  Summary: hits  131.289 ± 2.872M/s

  # UPROBE
  $ sudo ./bench -a trig-uprobe-without-nop
  Summary: hits    0.729 ± 0.007M/s

  $ sudo ./bench -a trig-uprobe-with-nop
  Summary: hits    1.798 ± 0.017M/s

  # URETPROBE
  $ sudo ./bench -a trig-uretprobe-without-nop
  Summary: hits    0.508 ± 0.012M/s

  $ sudo ./bench -a trig-uretprobe-with-nop
  Summary: hits    0.883 ± 0.008M/s

So there is almost 2.5x performance difference between probing nop vs
non-nop instruction for entry uprobe. And 1.7x difference for uretprobe.

This means that non-nop uprobe overhead is around 1.4 microseconds for uprobe
and 2 microseconds for non-nop uretprobe.

For nop variants, uprobe and uretprobe overhead is down to 0.556 and
1.13 microseconds, respectively.

For comparison, just doing a very low-overhead syscall (with no BPF
programs attached anywhere) gives:

  $ sudo ./bench trig-base -a
  Summary: hits    4.830 ± 0.036M/s

So uprobes are about 2.67x slower than pure context switch.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211116013041.4072571-1-andrii@kernel.org

tools/testing/selftests/bpf/Makefile

@@ -533,7 +533,9 @@ $(OUTPUT)/bench_ringbufs.o: $(OUTPUT)/ringbuf_bench.skel.h \
 $(OUTPUT)/bench_bloom_filter_map.o: $(OUTPUT)/bloom_filter_bench.skel.h
 $(OUTPUT)/bench.o: bench.h testing_helpers.h $(BPFOBJ)
 $(OUTPUT)/bench: LDLIBS += -lm
-$(OUTPUT)/bench: $(OUTPUT)/bench.o $(OUTPUT)/testing_helpers.o \
+$(OUTPUT)/bench: $(OUTPUT)/bench.o \
+		 $(OUTPUT)/testing_helpers.o \
+		 $(OUTPUT)/trace_helpers.o \
 		 $(OUTPUT)/bench_count.o \
 		 $(OUTPUT)/bench_rename.o \
 		 $(OUTPUT)/bench_trigger.o \

tools/testing/selftests/bpf/bench.c

@@ -359,6 +359,11 @@ extern const struct bench bench_trig_kprobe;
 extern const struct bench bench_trig_fentry;
 extern const struct bench bench_trig_fentry_sleep;
 extern const struct bench bench_trig_fmodret;
+extern const struct bench bench_trig_uprobe_base;
+extern const struct bench bench_trig_uprobe_with_nop;
+extern const struct bench bench_trig_uretprobe_with_nop;
+extern const struct bench bench_trig_uprobe_without_nop;
+extern const struct bench bench_trig_uretprobe_without_nop;
 extern const struct bench bench_rb_libbpf;
 extern const struct bench bench_rb_custom;
 extern const struct bench bench_pb_libbpf;
@@ -385,6 +390,11 @@ static const struct bench *benchs[] = {
 	&bench_trig_fentry,
 	&bench_trig_fentry_sleep,
 	&bench_trig_fmodret,
+	&bench_trig_uprobe_base,
+	&bench_trig_uprobe_with_nop,
+	&bench_trig_uretprobe_with_nop,
+	&bench_trig_uprobe_without_nop,
+	&bench_trig_uretprobe_without_nop,
 	&bench_rb_libbpf,
 	&bench_rb_custom,
 	&bench_pb_libbpf,

tools/testing/selftests/bpf/benchs/bench_trigger.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2020 Facebook */
 #include "bench.h"
 #include "trigger_bench.skel.h"
+#include "trace_helpers.h"
 
 /* BPF triggering benchmarks */
 static struct trigger_ctx {
@@ -107,6 +108,101 @@ static void *trigger_consumer(void *input)
 	return NULL;
 }
 
+/* make sure call is not inlined and not avoided by compiler, so __weak and
+ * inline asm volatile in the body of the function
+ *
+ * There is a performance difference between uprobing at nop location vs other
+ * instructions. So use two different targets, one of which starts with nop
+ * and another doesn't.
+ *
+ * GCC doesn't generate stack setup preample for these functions due to them
+ * having no input arguments and doing nothing in the body.
+ */
+__weak void uprobe_target_with_nop(void)
+{
+	asm volatile ("nop");
+}
+
+__weak void uprobe_target_without_nop(void)
+{
+	asm volatile ("");
+}
+
+static void *uprobe_base_producer(void *input)
+{
+	while (true) {
+		uprobe_target_with_nop();
+		atomic_inc(&base_hits.value);
+	}
+	return NULL;
+}
+
+static void *uprobe_producer_with_nop(void *input)
+{
+	while (true)
+		uprobe_target_with_nop();
+	return NULL;
+}
+
+static void *uprobe_producer_without_nop(void *input)
+{
+	while (true)
+		uprobe_target_without_nop();
+	return NULL;
+}
+
+static void usetup(bool use_retprobe, bool use_nop)
+{
+	size_t uprobe_offset;
+	ssize_t base_addr;
+	struct bpf_link *link;
+
+	setup_libbpf();
+
+	ctx.skel = trigger_bench__open_and_load();
+	if (!ctx.skel) {
+		fprintf(stderr, "failed to open skeleton\n");
+		exit(1);
+	}
+
+	base_addr = get_base_addr();
+	if (use_nop)
+		uprobe_offset = get_uprobe_offset(&uprobe_target_with_nop, base_addr);
+	else
+		uprobe_offset = get_uprobe_offset(&uprobe_target_without_nop, base_addr);
+
+	link = bpf_program__attach_uprobe(ctx.skel->progs.bench_trigger_uprobe,
+					  use_retprobe,
+					  -1 /* all PIDs */,
+					  "/proc/self/exe",
+					  uprobe_offset);
+	if (!link) {
+		fprintf(stderr, "failed to attach uprobe!\n");
+		exit(1);
+	}
+	ctx.skel->links.bench_trigger_uprobe = link;
+}
+
+static void uprobe_setup_with_nop()
+{
+	usetup(false, true);
+}
+
+static void uretprobe_setup_with_nop()
+{
+	usetup(true, true);
+}
+
+static void uprobe_setup_without_nop()
+{
+	usetup(false, false);
+}
+
+static void uretprobe_setup_without_nop()
+{
+	usetup(true, false);
+}
+
 const struct bench bench_trig_base = {
 	.name = "trig-base",
 	.validate = trigger_validate,
@@ -182,3 +278,53 @@ const struct bench bench_trig_fmodret = {
 	.report_progress = hits_drops_report_progress,
 	.report_final = hits_drops_report_final,
 };
+
+const struct bench bench_trig_uprobe_base = {
+	.name = "trig-uprobe-base",
+	.setup = NULL, /* no uprobe/uretprobe is attached */
+	.producer_thread = uprobe_base_producer,
+	.consumer_thread = trigger_consumer,
+	.measure = trigger_base_measure,
+	.report_progress = hits_drops_report_progress,
+	.report_final = hits_drops_report_final,
+};
+
+const struct bench bench_trig_uprobe_with_nop = {
+	.name = "trig-uprobe-with-nop",
+	.setup = uprobe_setup_with_nop,
+	.producer_thread = uprobe_producer_with_nop,
+	.consumer_thread = trigger_consumer,
+	.measure = trigger_measure,
+	.report_progress = hits_drops_report_progress,
+	.report_final = hits_drops_report_final,
+};
+
+const struct bench bench_trig_uretprobe_with_nop = {
+	.name = "trig-uretprobe-with-nop",
+	.setup = uretprobe_setup_with_nop,
+	.producer_thread = uprobe_producer_with_nop,
+	.consumer_thread = trigger_consumer,
+	.measure = trigger_measure,
+	.report_progress = hits_drops_report_progress,
+	.report_final = hits_drops_report_final,
+};
+
+const struct bench bench_trig_uprobe_without_nop = {
+	.name = "trig-uprobe-without-nop",
+	.setup = uprobe_setup_without_nop,
+	.producer_thread = uprobe_producer_without_nop,
+	.consumer_thread = trigger_consumer,
+	.measure = trigger_measure,
+	.report_progress = hits_drops_report_progress,
+	.report_final = hits_drops_report_final,
+};
+
+const struct bench bench_trig_uretprobe_without_nop = {
+	.name = "trig-uretprobe-without-nop",
+	.setup = uretprobe_setup_without_nop,
+	.producer_thread = uprobe_producer_without_nop,
+	.consumer_thread = trigger_consumer,
+	.measure = trigger_measure,
+	.report_progress = hits_drops_report_progress,
+	.report_final = hits_drops_report_final,
+};

tools/testing/selftests/bpf/progs/trigger_bench.c

@@ -52,3 +52,10 @@ int bench_trigger_fmodret(void *ctx)
 	__sync_add_and_fetch(&hits, 1);
 	return -22;
 }
+
+SEC("uprobe/self/uprobe_target")
+int bench_trigger_uprobe(void *ctx)
+{
+	__sync_add_and_fetch(&hits, 1);
+	return 0;
+}