readprofile - a tool to read kernel profiling information
readprofile [ options ]
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 ease readability.
Available command line options are the following:
Specify a mapfile, which by default is /usr/src/linux/Sys-
tem.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.
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 read-
profile-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 pro-
filing 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.
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 func-
tion, 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
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
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 pro-
filing, you can specify "profile=2" (or another number) on the kernel
commandline. The number you specify is the two-exponent used as pro-
Profiling is disabled when interrupts are inhibited. This means that
many profiling ticks happen when interrupts are re-enabled. Watch out
for misleading information.
/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 :-)
4th Berkeley Distribution May 1996 READPROFILE(1)
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