Benchmark on one machine too extreme

Question

I run a basic benchmark on my machines:

time echo "scale=3000;4*a(1)" | bc -l

This computes Pi to 3000 decimal places. The general expected time in my experience is 35-60 seconds on a Raspberry Pi B+, 2, 3.

One of my machines is giving 24 seconds, which is far out of the ordinary. This machine is a Raspberry Pi 3. My other Pi 3s give a consistent 48 seconds. I have checked the governor (it is ondemand), boot config parameters and rebooted to make sure its clean.

I am not asking for alternative benchmark systems. I do know what I have is shakey (does not test multiple CPUs etc...), but the differences are surprising and consistent.

What could be causing such anomolous behavior?

UPDATE: I have started looking at the problem again. I used a fresh install of the OS and added extra programs one by one. It seems the slowdown happens when using the packages openmpi-bin and python-mpi4py. I am investigating further.

Answer 1

Running that command to bench your RPi is not so acurate. That command will burn 1/4 cores of your Pi, thats why you get weirds results. Try to activate all 4 cores at 100%.

I coded a small benchmark script for raspberry (multi-core benchmark), to test it just copy and paste this command on your RPi:

curl https://raw.githubusercontent.com/aikoncwd/rpi-benchmark/master/rpi-benchmark.sh | sudo bash

It will test your CPU, Memory and microSD-IO. Here is my result for my overclocked RPi3:

Raspberry Pi Benchmark Test
Author: AikonCWD

temp=39.2'C
arm_freq=1400
core_freq=550
sdram_freq=575
microsd_clock=91.667 MHz

Running CPU test...
    total time:                          15.0670s
    temp=54.8'C

Running MEMORY test...
    total time:                          2.1438s
    temp=55.8'C

Running THREADS test...
    total time:                          7.6511s
    temp=58.0'C

Running HDPARM test...
    Timing buffered disk reads: 114 MB in  3.04 seconds =  37.47 MB/sec
    temp=49.4'C

Running DD WRITE test...
    536870912 bytes (537 MB) copied, 15.2853 s, 35.1 MB/s
    temp=46.2'C

Running DD READ test...
    536870912 bytes (537 MB) copied, 14.2355 s, 37.7 MB/s
    temp=45.1'C


AikonCWD's rpi-benchmark completed!

Try to run this benchmark over all your RPies and compare/share results here.

Feel free to fork my script and edit the values for a more "hardcore" benchmark :)

Answer 2

For what it's worth, I just ran that same test on a stock Raspberry Pi 3B running Raspbian Jessie and it completed in 24.3 seconds. It took 73.4 s on a Model B rev 2 running Wheezy.

Unless you have an idea of the system load beforehand, this isn't a particularly good general benchmark. Arbitrary-precision decimal number handling is a slightly special case. Maybe take a look at Roy Longbottom's Raspberry Pi & Raspberry Pi 2 Benchmarks for some options.