path: root/tools/power/cpupower/bench/README-BENCH
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authorDominik Brodowski <linux@dominikbrodowski.net>2011-03-30 16:30:11 +0200
committerDominik Brodowski <linux@dominikbrodowski.net>2011-07-29 18:35:36 +0200
commit7fe2f6399a84760a9af8896ac152728250f82adb (patch)
treefa4bf236359b8d6d9f8d6ff823ddd3e839da5768 /tools/power/cpupower/bench/README-BENCH
parentLinux 3.0 (diff)
cpupowerutils - cpufrequtils extended with quite some features
CPU power consumption vs performance tuning is no longer limited to CPU frequency switching anymore: deep sleep states, traditional dynamic frequency scaling and hidden turbo/boost frequencies are tied close together and depend on each other. The first two exist on different architectures like PPC, Itanium and ARM, the latter (so far) only on X86. On X86 the APU (CPU+GPU) will only run most efficiently if CPU and GPU has proper power management in place. Users and Developers want to have *one* tool to get an overview what their system supports and to monitor and debug CPU power management in detail. The tool should compile and work on as many architectures as possible. Once this tool stabilizes a bit, it is intended to replace the Intel-specific tools in tools/power/x86 Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
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+This is cpufreq-bench, a microbenchmark for the cpufreq framework.
+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)
+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
+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.
+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 avarage 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