readprofile
read kernel profiling information
Synopsis
readprofile
[options]
add an example, a script, a trick and tips
examples
Browse the profiling buffer ordering by clock ticks:
readprofile | sort -nr | less
Print the 20 most loaded procedures:
readprofile | sort -nr +2 | head -20
Print only filesystem profile:
readprofile | grep _ext2
Look at all the kernel information, with ram addresses"
readprofile -av | less
Browse a ’freezed’ profile buffer for a non current kernel:
readprofile -p ~/profile.freeze -m /zImage.map.gz
Request profiling at 2kHz per CPU, and reset the profiling
buffer
sudo readprofile -M 20
description
The
readprofile command uses the /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.
Available
command line options are the following:
-m mapfile
Specify a mapfile, which by
default is /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.
-p
pro-file
Specify a different profiling
buffer, which by default is /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 /proc/profile file can be copied
using ’cat’ or ’cp’. There is no
more support for compressed profile buffers, like in
readprofile-1.1, because the program needs to know
the size of the buffer in advance.
-i
Info. This makes 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 -t
(terse) switch is used together with -i only
the decimal number is printed.
-a
Print all symbols in the mapfile. By default the
procedures with 0 reported ticks are not printed.
-b
Print individual histogram-bin counts.
-r
Reset the profiling buffer. This can only be invoked by
root, because /proc/profile is readable by everybody
but writable only by the superuser. However, you can make
readprofile setuid 0, in order to reset the buffer
without gaining privileges.
-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.
-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.
-V
Version. This makes readprofile print its version
number and exit.
availability
The readprofile command is part of the util-linux package and is
available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
files
/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 :-)
version
This manpage documents version 2.0 of the program.
bugs
readprofile
only works with an 1.3.x or newer kernel, because
/proc/profile changed in the step from 1.2 to 1.3
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.
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.
Profiling is
disabled when interrupts are inhibited. This means that many
profiling ticks happen when interrupts are re-enabled. Watch
out for misleading information.