selftests/bpf: Add benchmark for local_storage RCU Tasks Trace usage

This benchmark measures grace period latency and kthread cpu usage of
RCU Tasks Trace when many processes are creating/deleting BPF
local_storage. Intent here is to quantify improvement on these metrics
after Paul's recent RCU Tasks patches [0].

Specifically, fork 15k tasks which call a bpf prog that creates/destroys
task local_storage and sleep in a loop, resulting in many
call_rcu_tasks_trace calls.

To determine grace period latency, trace time elapsed between
rcu_tasks_trace_pregp_step and rcu_tasks_trace_postgp; for cpu usage
look at rcu_task_trace_kthread's stime in /proc/PID/stat.

On my virtualized test environment (Skylake, 8 cpus) benchmark results
demonstrate significant improvement:

BEFORE Paul's patches:

  SUMMARY tasks_trace grace period latency        avg 22298.551 us stddev 1302.165 us
  SUMMARY ticks per tasks_trace grace period      avg 2.291 stddev 0.324

AFTER Paul's patches:

  SUMMARY tasks_trace grace period latency        avg 16969.197 us  stddev 2525.053 us
  SUMMARY ticks per tasks_trace grace period      avg 1.146 stddev 0.178

Note that since these patches are not in bpf-next benchmarking was done
by cherry-picking this patch onto rcu tree.

  [0] https://lore.kernel.org/rcu/20220620225402.GA3842369@paulmck-ThinkPad-P17-Gen-1/

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220705190018.3239050-1-davemarchevsky@fb.com

1 files changed, 67 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/local_storage_rcu_tasks_trace_bench.c b/tools/testing/selftests/bpf/progs/local_storage_rcu_tasks_trace_bench.c
new file mode 100644
index 000000000000..03bf69f49075
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/local_storage_rcu_tasks_trace_bench.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, int);
+} task_storage SEC(".maps");
+
+long hits;
+long gp_hits;
+long gp_times;
+long current_gp_start;
+long unexpected;
+bool postgp_seen;
+
+SEC("fentry/" SYS_PREFIX "sys_getpgid")
+int get_local(void *ctx)
+{
+	struct task_struct *task;
+	int idx;
+	int *s;
+
+	idx = 0;
+	task = bpf_get_current_task_btf();
+	s = bpf_task_storage_get(&task_storage, task, &idx,
+				 BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!s)
+		return 0;
+
+	*s = 3;
+	bpf_task_storage_delete(&task_storage, task);
+	__sync_add_and_fetch(&hits, 1);
+	return 0;
+}
+
+SEC("fentry/rcu_tasks_trace_pregp_step")
+int pregp_step(struct pt_regs *ctx)
+{
+	current_gp_start = bpf_ktime_get_ns();
+	return 0;
+}
+
+SEC("fentry/rcu_tasks_trace_postgp")
+int postgp(struct pt_regs *ctx)
+{
+	if (!current_gp_start && postgp_seen) {
+		/* Will only happen if prog tracing rcu_tasks_trace_pregp_step doesn't
+		 * execute before this prog
+		 */
+		__sync_add_and_fetch(&unexpected, 1);
+		return 0;
+	}
+
+	__sync_add_and_fetch(&gp_times, bpf_ktime_get_ns() - current_gp_start);
+	__sync_add_and_fetch(&gp_hits, 1);
+	current_gp_start = 0;
+	postgp_seen = true;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";