readprofile.1

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.TH READPROFILE 1 "May 1996"
.UC 4
.SH NAME
readprofile - a tool to read kernel profiling information
.SH SYNOPSIS
.B readprofile
[
.I options
]

.SH VERSION
This manpage documents version 2.0 of the program.

.SH DESCRIPTION

.LP
The
.B readprofile
command uses the 
.B /proc/profile
information to print ascii data on standard output.
The output is
organized in three columns: the first is the number of clock ticks,
the second is the name of the C function in the kernel where those many
ticks occurred, and the third is the normalized `load' of the procedure,
calculated as a ratio between the number of ticks and the length of
the procedure. The output is filled with blanks to ease readability.

.LP
Available command line options are the following:

.TP
.RB -m " mapfile"
Specify a mapfile, which by default is
.B /usr/src/linux/System.map.
You should specify the map file on cmdline if your current kernel isn't the
last one you compiled, or if you keep System.map elsewhere. If the name of
the map file ends with `.gz' it is decompressed on the fly.

.TP
.RB -p " pro-file"
Specify a different profiling buffer, which by default is
.B /proc/profile.
Using a different pro-file is useful if you want to `freeze' the
kernel profiling at some time and read it later. The
.B /proc/profile
file can be copied using `cat' or `cp'. There is no more support for
compressed profile buffers, like in 
.B readprofile-1.1,
because the program needs to know the size of the buffer in advance.

.TP
.B -i
Info. This makes 
.B readprofile
only print the profiling step used by the kernel.
The profiling step is the resolution of the profiling buffer, and
is chosen during kernel configuration (through `make config'),
or in the kernel's command line.
If the 
.B -t
(terse) switch is used together with
.B -i
only the decimal number is printed.

.TP
.B -a
Print all symbols in the mapfile. By default the procedures with 0 reported
ticks are not printed.

.TP
.B -b
Print individual histogram-bin counts.

.TP
.B -r
Reset the profiling buffer. This can only be invoked by root, because
.B /proc/profile
is readable by everybody but writable only by the superuser. However,
you can make 
.B readprofile
setuid 0, in order to reset the buffer without gaining privileges.

.TP
.RB -M " multiplier"
On some architectures it is possible to alter the frequency at which
the kernel delivers profiling interrupts to each CPU.  This option allows you to
set the frequency, as a multiplier of the system clock frequency, HZ.
This is supported on i386-SMP (2.2 and 2.4 kernel) and also on sparc-SMP
and sparc64-SMP (2.4 kernel).  This option also resets the profiling buffer,
and requires superuser privileges.

.TP
.B -v
Verbose. The output is organized in four columns and filled with blanks.
The first column is the RAM address of a kernel function, the second is
the name of the function, the third is the number of clock ticks and the
last is the normalized load.

.TP
.B -V
Version. This makes
.B readprofile
print its version number and exit.

.SH EXAMPLES
Browse the profiling buffer ordering by clock ticks:
.nf
   readprofile | sort -nr | less

.fi
Print the 20 most loaded procedures:
.nf
   readprofile | sort -nr +2 | head -20

.fi
Print only filesystem profile:
.nf
   readprofile | grep _ext2

.fi
Look at all the kernel information, with ram addresses"
.nf
   readprofile -av | less

.fi
Browse a `freezed' profile buffer for a non current kernel:
.nf
   readprofile -p ~/profile.freeze -m /zImage.map.gz

.fi
Request profiling at 2kHz per CPU, and reset the profiling buffer
.nf
   sudo readprofile -M 20

.fi

.SH BUGS

.LP
.B readprofile
only works with an 1.3.x or newer kernel,
because 
.B /proc/profile
changed in the step from 1.2 to 1.3

.LP
This program only works with ELF kernels. The change for a.out kernels
is trivial, and left as an exercise to the a.out user.

.LP
To enable profiling, the kernel must be rebooted, because no profiling module
is available, and it wouldn't be easy to build. To enable profiling,
you can specify "profile=2" (or another number) on the kernel commandline.
The number you specify is the two-exponent used as profiling step.

.LP
Profiling is disabled when interrupts are inhibited. This means that many
profiling ticks happen when interrupts are re-enabled. Watch out for
misleading information.

.SH FILES
.nf
/proc/profile              A binary snapshot of the profiling buffer.
/usr/src/linux/System.map  The symbol table for the kernel.
/usr/src/linux/*           The program being profiled :-)
.fi