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diff --git a/tools/power/cpupower/bench/README-BENCH b/tools/power/cpupower/bench/README-BENCH new file mode 100644 index 000000000..97727aed6 --- /dev/null +++ b/tools/power/cpupower/bench/README-BENCH @@ -0,0 +1,124 @@ +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=<long int> initial load time in us +-s, --sleep=<long int> initial sleep time in us +-x, --load-step=<long int> time to be added to load time, in us +-y, --sleep-step=<long int> time to be added to sleep time, in us +-c, --cpu=<unsigned int> CPU Number to use, starting at 0 +-p, --prio=<priority> scheduler priority, HIGH, LOW or DEFAULT +-g, --governor=<governor> cpufreq governor to test +-n, --cycles=<int> load/sleep cycles to get an average value to compare +-r, --rounds<int> load/sleep rounds +-f, --file=<configfile> config file to use +-o, --output=<dir> 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 + |