Drazen Urch
7bd1550195
* Checkpoint * cpu cycle ffi * Rename * mixnode feature * Bundle libcpucycles
58 lines
1.9 KiB
Plaintext
58 lines
1.9 KiB
Plaintext
.\" Automatically generated by Pandoc 2.9.2.1
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.\"
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.TH "cpucycles" "3" "" "" ""
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.hy
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.SS NAME
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.PP
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cpucycles - count CPU cycles
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.SS SYNOPSIS
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.IP
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.nf
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\f[C]
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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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\f[R]
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.fi
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.PP
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Link with \f[C]-lcpucycles\f[R].
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Old systems may also need \f[C]-lrt\f[R].
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.SS DESCRIPTION
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.PP
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\f[C]cpucycles()\f[R] returns an estimate for the number of CPU cycles
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that have occurred since an unspecified time in the past (perhaps system
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boot, perhaps program startup).
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.PP
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Accessing true cycle counters can be difficult on some CPUs and
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operating systems.
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\f[C]cpucycles()\f[R] does its best to produce accurate results, but
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selects a low-precision counter if the only other option is failure.
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.PP
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\f[C]cpucycles_persecond()\f[R] returns an estimate for the number of
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CPU cycles per second.
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This estimate comes from \f[C]/etc/cpucyclespersecond\f[R] if that file
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exists, otherwise from various OS mechanisms, otherwise from the
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\f[C]cpucyclespersecond\f[R] environment variable if that is set,
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otherwise 2399987654.
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.PP
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\f[C]cpucycles_implementation()\f[R] returns the name of the counter in
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use: e.g., \f[C]\[dq]amd64-pmc\[dq]\f[R].
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.PP
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\f[C]cpucycles_version()\f[R] returns the \f[C]libcpucycles\f[R] version
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number as a string: e.g., \f[C]\[dq]20230115\[dq]\f[R].
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Results of \f[C]cpucycles_implementation()\f[R] should be interpreted
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relative to \f[C]cpucycles_version()\f[R].
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.PP
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\f[C]cpucycles\f[R] is actually a function pointer.
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The first call to \f[C]cpucycles()\f[R] or
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\f[C]cpucycles_persecond()\f[R] or \f[C]cpucycles_implementation()\f[R]
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selects one of the available counters and updates the
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\f[C]cpucycles\f[R] pointer accordingly.
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Subsequent calls to \f[C]cpucycles()\f[R] are thread-safe.
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.SS SEE ALSO
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.PP
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\f[B]gettimeofday\f[R](2), \f[B]clock_gettime\f[R](2)
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