netstacklat: Experiment with 2 nth packet sampling

Sample every 2-nth packet (50%)
 - Overhead: 6039419756 / 32219314 = 187.44 ns

Compared to local atomic-nth overead: 157.67 ns
 - approx 30 ns extra cost to sample 50% vs 3.12%

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>

Author: netoptimizer

examples/netstacklat.bpf.c

@@ -29,7 +29,7 @@ const __s64 TAI_OFFSET = (37LL * NS_PER_S);
 const struct netstacklat_bpf_config user_config = {
 	.network_ns = 0,
 	.filter_min_queue_len = 0, /* zero means filter is inactive */
-	.filter_nth_packet = 32, /* reduce recorded event to every nth packet, use power-of-2 */
+	.filter_nth_packet = 2, /* reduce recorded event to every nth packet, use power-of-2 */
 	.filter_pid = false,
 	.filter_ifindex = true,
 	.filter_cgroup = true,