OProfile Files

Overview
--------

OProfile is a system-wide profiler for Linux systems, capable of profiling
all running code at low overhead. OProfile is released under the GNU GPL.

For versions 0.9.7 and earlier, the profiler consists of a kernel driver
and a daemon for collecting sample data. In version 0.9.8, the kernel
driver/daemon method of collecting sample data is deprecated in favor of
profiling with the Linux Kernel Performance Events Subsystem (kernel version
2.6.31 or higher). Several post-profiling tools for turning profile data
into human readable information are available.

OProfile leverages the hardware performance counters of the CPU to enable
profiling of a wide variety of interesting statistics, which can also be
used for basic time-spent profiling. All code is profiled: hardware and
software interrupt handlers, kernel modules, the kernel, shared libraries,
and applications.

OProfile is currently in alpha status; however it has proven stable over a
large number of differing configurations; it is being used on machines
ranging from laptops to 16-way NUMA-Q boxes. As always, there is no
warranty.


Features
--------

Unobtrusive
    - No special recompilations, wrapper libraries or the like are necessary.
      Even debug symbols (-g option to gcc) are not necessary unless you want
      to produce annotated source.
    - Kernel patches are usually unnecessary, except in cases where the
      running kernel may not yet support some newer processor models. 

System-wide profiling
    All code running on the system is profiled, enabling analysis of system
    performance. Note: Root authority is required to do system-wide
    profiling.
 
Single-process profiling
    Application developers will find the single-process profiling feature
    very convenient since it does not require root authority, and profile
    data is collected only for the specified process (or command). This
    method has the added benefit of "following" fork/execs and collecting
    profile information on those child processes as well. Note: This method
    of profiling requires a kernel version of 2.6.31 or higher. 

Performance counter support
    Enables collection of various low-level data, and assocation with
    particular sections of code. 

Call-graph support
    With an x86 or ARM 2.6 kernel, OProfile can provide gprof-style
    call-graph profiling data.

Low overhead
    OProfile has a typical overhead of 1-8%, dependent on sampling
    frequency and workload. 

Post-profile analysis
    Profile data can be produced on the function-level or instruction-
    level detail. Source trees annotated with profile information can be
    created. A hit list of applications and functions that take the most
    time across the whole system can be produced. 

System support
    OProfile works across a range of CPUs, include the Intel range, AMD's
    Athlon and AMD64 processors range, the Alpha, ARM, IBM PowerPC and
    more. OProfile will work against almost any 2.2, 2.4 and 2.6 kernels,
    and works on both UP and SMP systems from desktops to the scariest
    NUMAQ boxes. Note: As of version 0.9.8, only 2.6 kernels are supported.


History
-------

The early versions of OProfile were developed as part credit for an M.Sc. in
Computer Science. The basic principles of the design were inspired by Compaq's
profiler.