[Bug 570389] [NEW] Enable ftrace function profiler

[Chase Douglas]

Public bug reported:

SRU Justification:

Impact: Without function profiling we may have a more difficult time
resolving performance issues.

How Addressed: The ftrace function profiler is turned on in the common
kernel configs.

Reproduction: No ftrace function profiling is possible on current Ubuntu
10.04 LTS kernel. If it were, the file
/sys/kernel/debug/tracing/function_profile_enabled would exist.

Regression Potential: Enabling this functionality is an added bonus to
Ubuntu that should not cause any regressions. Further, regressions
should be localized to the ftrace subsystem, which will not affect the
vast majority of users.

=====

The ftrace framework has profiling capabilities that will be useful in
tracking desktop responsiveness. As an example, profiling can tell us
how many times an ISR is run, and how long the average run time is.

This option will not have any performance impact. When turned on at
runtime, a small performance impact may be seen, and a few hundred KB
per cpu of buffer pages will be allocated and used.

Extremely brief overview:

echo 1 > /sys/kernel/debug/tracing/function_profile_enabled
... run tests ...
echo 0 > /sys/kernel/debug/tracing/function_profile_enabled
cat /sys/kernel/debug/tracing/trace_stat/function0 (suffix: cpu #)

** Affects: linux (Ubuntu)
     Importance: Wishlist
     Assignee: Chase Douglas (chasedouglas)
         Status: In Progress


** Tags: lucid patch

-- 
Enable ftrace function profiler
https://bugs.launchpad.net/bugs/570389
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