readprofile - read kernel profiling information
This manpage documents version 2.0 of the program.
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
Print all symbols in the mapfile. By default the
procedures with reported ticks are not printed.
Print individual histogram-bin counts.
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
-m, --mapfile 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.
-M, --multiplier 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. Linux 2.6.16 dropped multiplier support for most systems. This
option also resets the profiling buffer, and requires superuser
-p, --profile pro-file
Specify a different profiling buffer, which by default is
. Using a different pro-file is useful if you want to
`freeze' the kernel profiling at some time and read it later. The
file can be copied using cat(1)
There is no more support for compressed profile buffers, like in
, because the program needs to know the size of the
buffer in advance.
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 set-user-ID 0, in
order to reset the buffer without gaining privileges.
Print individual counters within functions.
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.
Display version information and exit.
Display help text and exit.
A binary snapshot of the profiling buffer.
The symbol table for the kernel.
The program being profiled :-)
readprofile only works with a 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.
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:
Look at all the kernel information, with ram addresses:
Browse a 'frozen' 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