selftests/bpf: Add bpf-nop benchmark for timing overhead baseline

Add a minimal benchmark that measures the overhead of the batch-timing
infrastructure itself. The BPF program runs an empty BENCH_BPF_LOOP body
(~1.5-2 ns/op), establishing the floor cost that all timing-library
benchmarks include.

[root@virtme-ng tools/testing/selftests/bpf]# sudo ./bench -a -p8 bpf-nop
Setting up benchmark 'bpf-nop'...
Benchmark 'bpf-nop' started.
bpf-nop: median 1.82 ns/op, stddev 0.01, p99 1.86 (1754 samples)

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260427232313.1582588-4-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -906,6 +906,7 @@ $(OUTPUT)/bench_htab_mem.o: $(OUTPUT)/htab_mem_bench.skel.h
 $(OUTPUT)/bench_bpf_crypto.o: $(OUTPUT)/crypto_bench.skel.h
 $(OUTPUT)/bench_sockmap.o: $(OUTPUT)/bench_sockmap_prog.skel.h
 $(OUTPUT)/bench_lpm_trie_map.o: $(OUTPUT)/lpm_trie_bench.skel.h $(OUTPUT)/lpm_trie_map.skel.h
+$(OUTPUT)/bench_bpf_nop.o: $(OUTPUT)/bpf_nop_bench.skel.h bench_bpf_timing.h
 $(OUTPUT)/bench_bpf_timing.o: bench_bpf_timing.h
 $(OUTPUT)/bench.o: bench.h testing_helpers.h $(BPFOBJ)
 $(OUTPUT)/bench: LDLIBS += -lm
@@ -930,6 +931,7 @@ $(OUTPUT)/bench: $(OUTPUT)/bench.o \
 		 $(OUTPUT)/bench_sockmap.o \
 		 $(OUTPUT)/bench_lpm_trie_map.o \
 		 $(OUTPUT)/bench_bpf_timing.o \
+		 $(OUTPUT)/bench_bpf_nop.o \
 		 $(OUTPUT)/usdt_1.o \
 		 $(OUTPUT)/usdt_2.o \
 		 #

tools/testing/selftests/bpf/bench.c

@@ -575,6 +575,7 @@ extern const struct bench bench_lpm_trie_insert;
 extern const struct bench bench_lpm_trie_update;
 extern const struct bench bench_lpm_trie_delete;
 extern const struct bench bench_lpm_trie_free;
+extern const struct bench bench_bpf_nop;
 
 static const struct bench *benchs[] = {
 	&bench_count_global,
@@ -653,6 +654,7 @@ static const struct bench *benchs[] = {
 	&bench_lpm_trie_update,
 	&bench_lpm_trie_delete,
 	&bench_lpm_trie_free,
+	&bench_bpf_nop,
 };
 
 static void find_benchmark(void)

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

@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include "bench.h"
+#include "bench_bpf_timing.h"
+#include "bpf_nop_bench.skel.h"
+#include "bpf_util.h"
+
+static struct ctx {
+	struct bpf_nop_bench *skel;
+	struct bpf_bench_timing timing;
+	int prog_fd;
+} ctx;
+
+static void nop_validate(void)
+{
+	if (env.consumer_cnt != 0) {
+		fprintf(stderr, "benchmark doesn't support consumers\n");
+		exit(1);
+	}
+}
+
+static void nop_run_once(void *unused __always_unused)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+	bpf_prog_test_run_opts(ctx.prog_fd, &topts);
+}
+
+static void nop_setup(void)
+{
+	struct bpf_nop_bench *skel;
+	int err;
+
+	setup_libbpf();
+
+	skel = bpf_nop_bench__open();
+	if (!skel) {
+		fprintf(stderr, "failed to open skeleton\n");
+		exit(1);
+	}
+
+	err = bpf_nop_bench__load(skel);
+	if (err) {
+		fprintf(stderr, "failed to load skeleton: %s\n", strerror(-err));
+		bpf_nop_bench__destroy(skel);
+		exit(1);
+	}
+
+	ctx.skel = skel;
+	ctx.prog_fd = bpf_program__fd(skel->progs.bench_nop);
+
+	BENCH_TIMING_INIT(&ctx.timing, skel, 0);
+	bpf_bench_calibrate(&ctx.timing, nop_run_once, NULL);
+
+	env.duration_sec = 600;
+}
+
+static void *nop_producer(void *input)
+{
+	while (true)
+		nop_run_once(NULL);
+
+	return NULL;
+}
+
+static void nop_measure(struct bench_res *res)
+{
+	bpf_bench_timing_measure(&ctx.timing, res);
+}
+
+static void nop_report_final(struct bench_res res[], int res_cnt)
+{
+	bpf_bench_timing_report(&ctx.timing, "bpf-nop", NULL);
+}
+
+const struct bench bench_bpf_nop = {
+	.name		= "bpf-nop",
+	.validate	= nop_validate,
+	.setup		= nop_setup,
+	.producer_thread = nop_producer,
+	.measure	= nop_measure,
+	.report_final	= nop_report_final,
+};

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

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bench_bpf_timing.bpf.h"
+
+SEC("syscall")
+int bench_nop(void *ctx)
+{
+	return BENCH_BPF_LOOP(0, ({}));
+}
+
+char _license[] SEC("license") = "GPL";