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.TH KPROF 3
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.SH NAME
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kprof \- kernel profiling
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.SH SYNOPSIS
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.nf
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.B bind -a #K /dev
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.sp
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.B /dev/kpctl
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.B /dev/kpdata
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.fi
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.SH DESCRIPTION
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The
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.I kprof
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device provides simple profiling
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data for the operating system kernel.   The data accumulates by
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recording the program counter of the kernel at each `tick' of the
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system clock.
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.PP
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The file
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.B kpdata
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holds the accumulated counts as 4-byte integers in big-endian
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byte order.
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The size of the file depends on the size of kernel text.
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The first count
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holds the total number of clock ticks during profiling;
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the second the number of ticks that occurred while the kernel
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was running.  The rest each hold the number of ticks
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the kernel program counter was within the
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corresponding 8-byte range of kernel text, starting from the base
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of kernel text.
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.PP
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The file
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.B kpctl
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controls profiling.
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Writing the string
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.B start
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to
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.B kpctl
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begins profiling;
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.B stop
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terminates it.  The message
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.B startclr
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restarts profiling after zeroing the array of counts.
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.PP
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The program
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.I kprof
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(see
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.IR prof (1))
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formats the data for presentation.
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.SH EXAMPLE
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The following
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.IR rc (1)
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script runs a test program while profiling the kernel
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and reports the results.
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.sp
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.EX
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	bind -a '#K' /dev
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	echo start > /dev/kpctl
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	runtest
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	echo stop > /dev/kpctl
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	kprof /386/9pcdisk /dev/kpdata
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.EE
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.SH SOURCE
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.B /sys/src/9/port/devkprof.c
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.SH SEE ALSO
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.IR prof (1)