Re: [PATCH v2 2/2] selftests/pipe: add pipe_bench microbenchmark

[Oleg Nesterov <oleg@redhat.com>]

On 05/22, Breno Leitao wrote:
>
> Add a small selftest that stresses pipe->mutex contention by spawning N
> writer threads that hammer a single pipe with multi-page writes, plus M
> reader threads that drain. Each writer records its own write() latency
> samples into a log2-bucketed histogram; main aggregates and prints
> total writes, throughput, average and percentile (p50/p99) latencies,
> and the maximum observed latency.
> 
> Pass --memory-pressure to fork stress-ng (--vm 4 --vm-bytes 80%
> --vm-method all) for the duration of the run, so alloc_page() in
> anon_pipe_write() routinely hits direct reclaim. The flag fails
> fast if stress-ng is not on $PATH.
> 
> Program print something like the following, for different writes,
> readers, msgsizes and memory pressure:
> 
> 	config: writers=X readers=Y msgsize=Z duration=3 pipe_size=1048576
> 	memory_pressure=[no|yes]
> 	writes: total=54451 rate=18150/s
> 	throughput_MBps: 1134.40
> 	lat_avg_ns: 275355
> 	lat_p50_ns_upper: 262143
> 	lat_p99_ns_upper: 1048575
> 	lat_max_ns: 2145633


The more tests the better... but since it comes as 2/2, perhaps the changelog
could mention the difference before/after 1/2 according to this test?

Oleg.