82 lines
3.5 KiB
Plaintext
82 lines
3.5 KiB
Plaintext
This component implements a CPU service which samples the instruction pointer
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of the configured threads on a regular basis for the purpose of statistical
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profiling.
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The collected samples are written to the LOG session with an individual label
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for each thread. By using the 'fs_log' component, the sample data can be
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written into separate files if desired.
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Configuration options
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---------------------
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! <config sample_interval_ms="100" sample_duration_s="1">
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! <policy label="init -> test-cpu_sampler -> ep" />
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! </config>
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The 'sample_interval_ms' attribute configures the time between two samples in
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milliseconds.
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The 'sample_duration_s' attribute configures the overall duration of the
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sampling activity in seconds.
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The policy configures the threads to be sampled.
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The clients of the CPU sampler component must be at least grand children of the
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initial init process to have their CPU sessions routed correctly. An example
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configuration using a sub-init process can be found in the 'cpu_sampler.run'
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script.
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Evaluation
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----------
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Currently, some basic tools for the evaluation of the sampled addresses are
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available at
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[https://github.com/cproc/genode_stuff/tree/cpu_sampler-16.08]
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* Filtering the sampled addresses from the Genode log output
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! filter_sampled_addresses_from_log <file containing the Genode log output>
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This script extracts the sampled addresses from a file containing the Genode
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log output and saves them in the file 'sampled_addresses.txt'. It is not
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needed when the addresses have already been written into a separate file by
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the 'fs_log' component. The match string (label) in the script might need to
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be adapted for the specific scenario.
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* Filtering the shared library load addresses from the Genode log output
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! filter_ldso_addresses_from_log <file containing the Genode log output>
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This script extracts the shared library load addresses from a file containing
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the Genode log output and saves them in the file 'ldso_addresses.txt'. To have
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these addresses appear in the Genode log output, the sampled component should
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be configured with the 'ld_verbose="yes"' XML attribute if it uses shared
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libraries. If multiple components in a scenario are configured with this
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attribute, the script needs to be adapted to match a specific label.
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* Generating statistics
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! generate_statistics <ELF image> <file with sampled addresses> [<file with ldso addresses>]
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This script generates the files 'statistics_by_function.txt' and
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'statistics_by_address.txt'.
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The first argument is the name of the ELF image of the sampled component.
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The second argument is the name of a file containing the sampled addresses.
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The third argument is the name of a file containing the shared library load
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addresses. It is only needed if the sampled component uses shared libraries.
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The 'statistics_by_function.txt' file lists the names of the sampled
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functions, sorted by the highest sample count. Each line comprehends
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all sampled addresses which belong to the particular function.
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The 'statistics_by_address.txt' file is more detailed than the
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'statistics_by_function.txt' file. It lists the sampled addresses, sorted by
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the highest sample count, together with the name and file location of the
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function the particular address belongs to.
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The 'generate_statistics' script uses the 'backtrace' script to determine the
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function names and file locations. The best location to use the scripts is
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the 'build/.../bin' directory, where all the shared libraries can be found.
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