readprofile — a tool to read kernel profiling information
readprofile [options]
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
mapfileSpecify 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−fileSpecify 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.
−iInfo. 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.
−aPrint all symbols in the mapfile. By default the procedures with 0 reported ticks are not printed.
−bPrint individual histogram-bin counts.
−rReset 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
multiplierOn 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.
−vVerbose. 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.
−VVersion. This makes readprofile print its version number and exit.
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 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.