KPROF(3)KPROF(3)NAMEkprof - kernel profiling
SYNOPSIS
bind -a #T /dev
/dev/kpctl
/dev/kpdata
DESCRIPTION
The kprof device provides simple profiling data for the operating sys‐
tem kernel. The data accumulates by recording the program counter of
the kernel at each `tick' of a profiling clock. Often this is just the
system clock, but may be an independent higher priority timer which
allows profiling 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 buck‐
ets, 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 sample
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
}
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).
KPROF(3)
