Drazen Urch
7bd1550195
* Checkpoint * cpu cycle ffi * Rename * mixnode feature * Bundle libcpucycles
48 lines
1.6 KiB
Markdown
48 lines
1.6 KiB
Markdown
### NAME
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cpucycles - count CPU cycles
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### SYNOPSIS
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#include <cpucycles.h>
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long long count = cpucycles();
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long long persecond = cpucycles_persecond();
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const char *implementation = cpucycles_implementation();
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const char *version = cpucycles_version();
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Link with `-lcpucycles`. Old systems may also need `-lrt`.
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### DESCRIPTION
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`cpucycles()` returns an estimate for the number of CPU cycles that have
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occurred since an unspecified time in the past (perhaps system boot,
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perhaps program startup).
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Accessing true cycle counters can be difficult on some CPUs and
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operating systems. `cpucycles()` does its best to produce accurate
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results, but selects a low-precision counter if the only other option is
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failure.
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`cpucycles_persecond()` returns an estimate for the number of CPU cycles
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per second. This estimate comes from `/etc/cpucyclespersecond` if that
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file exists, otherwise from various OS mechanisms, otherwise from the
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`cpucyclespersecond` environment variable if that is set, otherwise
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2399987654.
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`cpucycles_implementation()` returns the name of the counter in use:
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e.g., `"amd64-pmc"`.
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`cpucycles_version()` returns the `libcpucycles` version number as a
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string: e.g., `"20230115"`. Results of `cpucycles_implementation()`
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should be interpreted relative to `cpucycles_version()`.
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`cpucycles` is actually a function pointer. The first call to
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`cpucycles()` or `cpucycles_persecond()` or `cpucycles_implementation()`
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selects one of the available counters and updates the `cpucycles`
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pointer accordingly. Subsequent calls to `cpucycles()` are thread-safe.
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### SEE ALSO
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**gettimeofday**(2), **clock_gettime**(2)
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