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