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, 12 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/bench.h b/tools/testing/selftests/bpf/bench.h
index 4b15286753ba..d748255877e2 100644
--- a/tools/testing/selftests/bpf/bench.h
+++ b/tools/testing/selftests/bpf/bench.h
@@ -30,11 +30,19 @@ struct env {
 	struct cpu_set cons_cpus;
 };
 
+struct basic_stats {
+	double mean;
+	double stddev;
+};
+
 struct bench_res {
 	long hits;
 	long drops;
 	long false_hits;
 	long important_hits;
+	unsigned long gp_ns;
+	unsigned long gp_ct;
+	unsigned int stime;
 };
 
 struct bench {
@@ -65,6 +73,10 @@ void ops_report_final(struct bench_res res[], int res_cnt);
 void local_storage_report_progress(int iter, struct bench_res *res,
 				   long delta_ns);
 void local_storage_report_final(struct bench_res res[], int res_cnt);
+void grace_period_latency_basic_stats(struct bench_res res[], int res_cnt,
+				      struct basic_stats *gp_stat);
+void grace_period_ticks_basic_stats(struct bench_res res[], int res_cnt,
+				    struct basic_stats *gp_stat);
 
 static inline __u64 get_time_ns(void)
 {