selftests/bpf/benchs: Add overwrite mode benchmark for BPF ring buffer

selftests/bpf/benchs: Add overwrite mode benchmark for BPF ring buffer

Add --rb-overwrite option to benchmark BPF ring buffer in overwrite mode.
Since overwrite mode is not yet supported by libbpf for consumer, also add
--rb-bench-producer option to benchmark producer directly without a consumer.

Benchmarks on an x86_64 and an arm64 CPU are shown below for reference.

- AMD EPYC 9654 (x86_64)

Ringbuf, multi-producer contention in overwrite mode, no consumer
=================================================================
rb-prod nr_prod 1    32.180 ± 0.033M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 2    9.617 ± 0.003M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 3    8.810 ± 0.002M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 4    9.272 ± 0.001M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 8    9.173 ± 0.001M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 12   3.086 ± 0.032M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 16   2.945 ± 0.021M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 20   2.519 ± 0.021M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 24   2.545 ± 0.021M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 28   2.363 ± 0.024M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 32   2.357 ± 0.021M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 36   2.267 ± 0.011M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 40   2.284 ± 0.020M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 44   2.215 ± 0.025M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 48   2.193 ± 0.023M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 52   2.208 ± 0.024M/s (drops 0.000 ± 0.000M/s)

- HiSilicon Kunpeng 920 (arm64)

Ringbuf, multi-producer contention in overwrite mode, no consumer
=================================================================
rb-prod nr_prod 1    14.478 ± 0.006M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 2    21.787 ± 0.010M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 3    6.045 ± 0.001M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 4    5.352 ± 0.003M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 8    4.850 ± 0.002M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 12   3.542 ± 0.016M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 16   3.509 ± 0.021M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 20   3.171 ± 0.010M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 24   3.154 ± 0.014M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 28   2.974 ± 0.015M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 32   3.167 ± 0.014M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 36   2.903 ± 0.010M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 40   2.866 ± 0.010M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 44   2.914 ± 0.010M/s (drops 0.000 ± 0.000M/s)
rb-prod nr_prod 48   2.806 ± 0.012M/s (drops 0.000 ± 0.000M/s)
Rb-prod nr_prod 52   2.840 ± 0.012M/s (drops 0.000 ± 0.000M/s)

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20251018035738.4039621-4-xukuohai@huaweicloud.com