Enable custom prefix command from env var

I setup my machine with the kernel options to isolate a cpu
and then I have a custom script that writes to the necessary files,
and I have NOPASSWD sudo commands setup for the commands in that file.

Then I can set this env var to that script and it runs
benchmarks specifically configured for my machine with no sudo prompt.

Example script:

    #!/bin/bash

    # sudoers
    # rwstauner ALL= NOPASSWD: /usr/bin/tee /sys/devices/system/cpu/intel_pstate/no_turbo
    # rwstauner ALL= NOPASSWD: /usr/bin/tee /sys/devices/system/cpu/intel_pstate/min_perf_pct
    # rwstauner ALL= NOPASSWD: /usr/bin/tee /sys/devices/system/cpu/cpu*/online
    # rwstauner ALL= NOPASSWD: /usr/bin/renice

    # NOTE: add `isolcpus=10,11 nohz_full=10,11` to the options line in /boot/loader conf

    cpu=10
    sibling=11

    sudo () {
      command sudo --bell "$@"
    }

    teardown () {
      echo 0 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
      echo 8 | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct
      echo 1 | sudo tee /sys/devices/system/cpu/cpu$sibling/online
    }

    setup () {
      echo 1 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
      echo 100 | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct
      echo 0 | sudo tee /sys/devices/system/cpu/cpu$sibling/online
    }

    setup > /dev/null
    trap 'teardown > /dev/null' EXIT

    setarch x86_64 -R taskset -c $cpu sh -c 'sudo renice -n -15 "$$" > /dev/null; exec "$@"' - "$@"

Author: rwstauner

lib/benchmark_suite.rb

@@ -230,6 +230,10 @@ def linux?
 
   # Set up the base command with CPU pinning if needed
   def base_cmd(ruby_description, benchmark_name)
+    ENV["RUBY_BENCH_PREFIX_COMMAND"]&.tap do |var|
+      return [var] if var
+    end
+
     if linux?
       cmd = setarch_prefix