1 This is cpufreq-bench, a microbenchmark for the cpufreq framework. 2 3 Purpose 4 ======= 5 6 What is this benchmark for: 7 - Identify worst case performance loss when doing dynamic frequency 8 scaling using Linux kernel governors 9 - Identify average reaction time of a governor to CPU load changes 10 - (Stress) Testing whether a cpufreq low level driver or governor works 11 as expected 12 - Identify cpufreq related performance regressions between kernels 13 - Possibly Real time priority testing? -> what happens if there are 14 processes with a higher prio than the governor's kernel thread 15 - ... 16 17 What this benchmark does *not* cover: 18 - Power saving related regressions (In fact as better the performance 19 throughput is, the worse the power savings will be, but the first should 20 mostly count more...) 21 - Real world (workloads) 22 23 24 Description 25 =========== 26 27 cpufreq-bench helps to test the condition of a given cpufreq governor. 28 For that purpose, it compares the performance governor to a configured 29 powersave module. 30 31 32 How it works 33 ============ 34 You can specify load (100% CPU load) and sleep (0% CPU load) times in us which 35 will be run X time in a row (cycles): 36 37 sleep=25000 38 load=25000 39 cycles=20 40 41 This part of the configuration file will create 25ms load/sleep turns, 42 repeated 20 times. 43 44 Adding this: 45 sleep_step=25000 46 load_step=25000 47 rounds=5 48 Will increase load and sleep time by 25ms 5 times. 49 Together you get following test: 50 25ms load/sleep time repeated 20 times (cycles). 51 50ms load/sleep time repeated 20 times (cycles). 52 .. 53 100ms load/sleep time repeated 20 times (cycles). 54 55 First it is calibrated how long a specific CPU intensive calculation 56 takes on this machine and needs to be run in a loop using the performance 57 governor. 58 Then the above test runs are processed using the performance governor 59 and the governor to test. The time the calculation really needed 60 with the dynamic freq scaling governor is compared with the time needed 61 on full performance and you get the overall performance loss. 62 63 64 Example of expected results with ondemand governor: 65 66 This shows expected results of the first two test run rounds from 67 above config, you there have: 68 69 100% CPU load (load) | 0 % CPU load (sleep) | round 70 25 ms | 25 ms | 1 71 50 ms | 50 ms | 2 72 73 For example if ondemand governor is configured to have a 50ms 74 sampling rate you get: 75 76 In round 1, ondemand should have rather static 50% load and probably 77 won't ever switch up (as long as up_threshold is above). 78 79 In round 2, if the ondemand sampling times exactly match the load/sleep 80 trigger of the cpufreq-bench, you will see no performance loss (compare with 81 below possible ondemand sample kick ins (1)): 82 83 But if ondemand always kicks in in the middle of the load sleep cycles, it 84 will always see 50% loads and you get worst performance impact never 85 switching up (compare with below possible ondemand sample kick ins (2)):: 86 87 50 50 50 50ms ->time 88 load -----| |-----| |-----| |-----| 89 | | | | | | | 90 sleep |-----| |-----| |-----| |---- 91 |-----|-----|-----|-----|-----|-----|-----|---- ondemand sampling (1) 92 100 0 100 0 100 0 100 load seen by ondemand(%) 93 |-----|-----|-----|-----|-----|-----|-----|-- ondemand sampling (2) 94 50 50 50 50 50 50 50 load seen by ondemand(%) 95 96 You can easily test all kind of load/sleep times and check whether your 97 governor in average behaves as expected. 98 99 100 ToDo 101 ==== 102 103 Provide a gnuplot utility script for easy generation of plots to present 104 the outcome nicely. 105 106 107 cpufreq-bench Command Usage 108 =========================== 109 -l, --load=<long int> initial load time in us 110 -s, --sleep=<long int> initial sleep time in us 111 -x, --load-step=<long int> time to be added to load time, in us 112 -y, --sleep-step=<long int> time to be added to sleep time, in us 113 -c, --cpu=<unsigned int> CPU Number to use, starting at 0 114 -p, --prio=<priority> scheduler priority, HIGH, LOW or DEFAULT 115 -g, --governor=<governor> cpufreq governor to test 116 -n, --cycles=<int> load/sleep cycles to get an average value to compare 117 -r, --rounds<int> load/sleep rounds 118 -f, --file=<configfile> config file to use 119 -o, --output=<dir> output dir, must exist 120 -v, --verbose verbose output on/off 121 122 Due to the high priority, the application may not be responsible for some time. 123 After the benchmark, the logfile is saved in OUTPUTDIR/benchmark_TIMESTAMP.log 124
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