This is cpufreq-bench, a microbenchmark for the cpufreq framework. Purpose ======= What is this benchmark for: - Identify worst case performance loss when doing dynamic frequency scaling using Linux kernel governors - Identify average reaction time of a governor to CPU load changes - (Stress) Testing whether a cpufreq low level driver or governor works as expected - Identify cpufreq related performance regressions between kernels - Possibly Real time priority testing? -> what happens if there are processes with a higher prio than the governor's kernel thread - ... What this benchmark does *not* cover: - Power saving related regressions (In fact as better the performance throughput is, the worse the power savings will be, but the first should mostly count more...) - Real world (workloads) Description =========== cpufreq-bench helps to test the condition of a given cpufreq governor. For that purpose, it compares the performance governor to a configured powersave module. How it works ============ You can specify load (100% CPU load) and sleep (0% CPU load) times in us which will be run X time in a row (cycles): sleep=25000 load=25000 cycles=20 This part of the configuration file will create 25ms load/sleep turns, repeated 20 times. Adding this: sleep_step=25000 load_step=25000 rounds=5 Will increase load and sleep time by 25ms 5 times. Together you get following test: 25ms load/sleep time repeated 20 times (cycles). 50ms load/sleep time repeated 20 times (cycles). .. 100ms load/sleep time repeated 20 times (cycles). First it is calibrated how long a specific CPU intensive calculation takes on this machine and needs to be run in a loop using the performance governor. Then the above test runs are processed using the performance governor and the governor to test. The time the calculation really needed with the dynamic freq scaling governor is compared with the time needed on full performance and you get the overall performance loss. Example of expected results with ondemand governor: This shows expected results of the first two test run rounds from above config, you there have: 100% CPU load (load) | 0 % CPU load (sleep) | round 25 ms | 25 ms | 1 50 ms | 50 ms | 2 For example if ondemand governor is configured to have a 50ms sampling rate you get: In round 1, ondemand should have rather static 50% load and probably won't ever switch up (as long as up_threshold is above). In round 2, if the ondemand sampling times exactly match the load/sleep trigger of the cpufreq-bench, you will see no performance loss (compare with below possible ondemand sample kick ins (1)): But if ondemand always kicks in in the middle of the load sleep cycles, it will always see 50% loads and you get worst performance impact never switching up (compare with below possible ondemand sample kick ins (2)):: 50 50 50 50ms ->time load -----| |-----| |-----| |-----| | | | | | | | sleep |-----| |-----| |-----| |---- |-----|-----|-----|-----|-----|-----|-----|---- ondemand sampling (1) 100 0 100 0 100 0 100 load seen by ondemand(%) |-----|-----|-----|-----|-----|-----|-----|-- ondemand sampling (2) 50 50 50 50 50 50 50 load seen by ondemand(%) You can easily test all kind of load/sleep times and check whether your governor in average behaves as expected. ToDo ==== Provide a gnuplot utility script for easy generation of plots to present the outcome nicely. cpufreq-bench Command Usage =========================== -l, --load= initial load time in us -s, --sleep= initial sleep time in us -x, --load-step= time to be added to load time, in us -y, --sleep-step= time to be added to sleep time, in us -c, --cpu= CPU Number to use, starting at 0 -p, --prio= scheduler priority, HIGH, LOW or DEFAULT -g, --governor= cpufreq governor to test -n, --cycles= load/sleep cycles to get an average value to compare -r, --rounds load/sleep rounds -f, --file= config file to use -o, --output= output dir, must exist -v, --verbose verbose output on/off Due to the high priority, the application may not be responsible for some time. After the benchmark, the logfile is saved in OUTPUTDIR/benchmark_TIMESTAMP.log