c38fcb5dc3
We used to use performance cycle counter for cycles(), but it is kind of useless in userspace as each core has its own counter and hence not comparable between cores. Also, the cycle counter stops counting when the cores are idle. Most callers expect cycles() to return a high resolution timestamp instead, so do the best we can do here and enable the userspace generic timer virtual counter.
62 lines
1.2 KiB
Plaintext
62 lines
1.2 KiB
Plaintext
.TH CPUTIME 2
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.SH NAME
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cputime, times, cycles \- cpu time in this process and children
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLdouble 'u
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.B
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long times(long t[4])
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.PP
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.B
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double cputime(void)
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.PP
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.B
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void cycles(uvlong *cyclep)
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.SH DESCRIPTION
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If
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.I t
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is non-null,
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.I times
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fills it in
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with the number of milliseconds spent in user code, system calls,
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child processes in user code, and child processes in system calls.
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.I Cputime
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returns the sum of those same times, converted to seconds.
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.I Times
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returns the elapsed real time, in milliseconds, that the process has been running.
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.PP
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These functions read
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.BR /dev/cputime ,
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opening that file when they are first called.
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.PP
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.I Cycles
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reads the processor's timestamp counter of cycles since reset,
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if any, and stores it via
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.IR cyclep .
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Currently supported architectures are
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.BR 386 ,
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.BR amd64 ,
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.B arm64
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and
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.BR power ;
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on all others,
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.I cycles
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will store zero.
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.SH SOURCE
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.B /sys/src/libc/9sys
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.br
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.B /sys/src/libc/*/cycles.[cs]
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.SH SEE ALSO
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.IR exec (2),
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.IR cons (3)
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.SH BUGS
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Only
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.B 386
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processors starting with the Pentium have timestamp counters;
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calling
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.I cycles
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on earlier processors may execute an illegal instruction.
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