selftests/bpf: Filter timing outliers with IQR in batch-timing library

System noise (timer interrupts, scheduling) can inflate the reported
stddev. tcp-v4-syn showed stddev 37.86 ns without filteri

selftests/bpf: Filter timing outliers with IQR in batch-timing library

System noise (timer interrupts, scheduling) can inflate the reported
stddev. tcp-v4-syn showed stddev 37.86 ns without filtering vs
0.16 ns with filtering on the same run data.

Filter samples outside [Q1 - 1.5*IQR, Q3 + 1.5*IQR] before computing
statistics. Scenarios with genuinely wide distributions have large IQR
so the fences stay wide and the filter has minimal effect.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260520133338.3392667-4-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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selftests/bpf: Add BPF batch-timing library

Add a reusable timing library for BPF benchmarks that need to measure
BPF program execution time.

The BPF side (progs/bench_bpf_timing.bpf.h) provides pe

selftests/bpf: Add BPF batch-timing library

Add a reusable timing library for BPF benchmarks that need to measure
BPF program execution time.

The BPF side (progs/bench_bpf_timing.bpf.h) provides per-CPU sample
arrays and BENCH_BPF_LOOP(), a macro that brackets batch_iters
iterations with bpf_ktime_get_ns() reads and records the elapsed time.
One extra untimed iteration runs afterward for output validation.

The userspace side (benchs/bench_bpf_timing.c) collects samples from
the skeleton BSS, computes percentile statistics, and auto-calibrates
batch_iters to target ~10 ms per batch.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260427232313.1582588-3-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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