KPROF(3) KPROF(3)
NAME
kprof - kernel profiling
SYNOPSIS
bind -a #T /dev
/dev/kpctl
/dev/kpdata
DESCRIPTION
The kprof device provides simple profiling data for the
operating system kernel. The data accumulates by recording
the program counter of the kernel at each `tick' of a pro-
filing clock. Often this is just the system clock, but may
be an independent higher priority timer which allows profil-
ing of interrupt handlers, dependent on implementation.
The file kpdata holds the accumulated counts in big-endian
byte order. The size of the file depends on the size of
kernel text, and the size of the individual counts. The
first six counts are 4 bytes in size, and are special. The
first holds the total number of ticks, the second the number
of ticks which fell outside the kernel text, the third the
number of microseconds per tick, the fourth the number of
sample buckets, the fifth the size in bytes of each sample
bucket, and sixth the log base 2 of the sample bucket size.
Typically the sample size is 4, and the log base 2 of the
bucket size 3 (8 bytes). The remainder of the file holds the
sample buckets. The entire file has size sample bucket size
times number of sample buckets. That is, the first six sam-
ple buckets are replaced with the special numbers.
The file kpctl controls profiling. Writing the string start
to kpctl begins profiling; stop terminates it. The message
startclr restarts profiling after zeroing the array of
counts.
Kprof(10.1) formats the data for presentation.
EXAMPLE
The following sh(1) commands define and invoke a function
sample that runs a given test program with kernel profiling
enabled, and copies the result to a server presumed to be
mounted on /n/remote.
fn sample {
echo start >/dev/kpctl
$1
echo stop >/dev/kpctl
cp /dev/kpdata /n/remote/tmp/kpdata
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KPROF(3) KPROF(3)
}
bind -a '#T' /dev
sample {cp sound /dev/audio}
On the server, the kprof(10.1) command is used to analyse
the data:
kprof /usr/inferno/os/mpc/impc /tmp/kpdata
SOURCE
/os/port/devkprof.c
SEE ALSO
kprof(10.1)
BUGS
It cannot provide times for each node in the dynamic call
graph (dynamic profiling).
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