Ftrace Function Graph ARM

Revision as of 16:34, 17 November 2009 by Tim Bird (talk | contribs) (Patches: add info about __gnu_mcount_nc)
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This page holds information from Tim Bird's talk at Linux Symposium Montreal (July, 2009), and at ELC Europe and the Japan Linux Symposium (October, 2009).

In Canada, Tim talked about patches against the 2.6.31-rc1 kernel tree for adding function graph tracing to the ARM architecture, for the Ftrace system.

In France and Japan, Tim talked about patches against 2.6.32-rc5.


Here is the presentation from the Japan Linux Symposium (also given at ELC Europe, in Grenoble France)

Here is the presentation from the Canada Linux Symposium session:


Here is Tim's paper for the Canada Linux Symposium for this work:


See the file Documentation/trace/func-duration.txt, after applying the patches.

(Or, if you applied the 2.6.31 patches, see the file Documentation/trace/func-graph.txt However, this version is deprecated.)


Below are patches for the function graph support and function duration tracer, for two kernel versions.

Note recent ARM toolchains instrument the code with calls to '__gnu_mcount_nc' instead of 'mcount'. If you get a compiler warning about missing the symbol '__gnu_mcount_nc', you should apply the patch mentioned in this e-mail also: (

[Thanks to Jean Pihet of MontaVista for pointing this out]

2.6.32-rc5 patches

To apply, extract the patches and the series file. If you have 'quilt', extract the file directly into the top level of the kernel source tree (the top directory is called 'patches'). Then do "quilt push -a".

If you don't have quilt, apply the patches manually, in the order specified in the 'series' file, with a command like: "patch -p1 <patches/foo.patch"

2.6.31-rc1 patches

The following patches were submitted to the kernel mailing list in early July 2009. There are patches against kernel version 2.6.31-rc1.



The 'fdd' tool is now incorporated into the patch set, and is located in the kernel scripts directory after applying the patches. See the documentation in the kernel tree for instructions for use.


To install:

* Download
* rename to 'ftd': mv Ftd.txt ftd
* make it executable: chmod a+x
* Put it on your path somewhere: sudo mv ftd /usr/local/bin


Based on feeback from ftrace developers on the kernel mailing list, and from other developers at the tracing mini-summit in Montreal, I started working on an updated duration tracer, using a different filtering approach. This work was completed, and resulted in a new trace, the "function_duration" tracer, being completed in September of 2009.

This work was described at ELC Europe and the Japan Linux Symposium, in October, 2009. I was hoping to mainline the patches before the events, but ran out of time due to bugs on my main testing platform.

Further Work

I need to try to mainline this feature. I'd like to get it into Linux-tip or Linux-next sometime before the 2.6.33 merge window.

If you don't see it in mainline, just send me an e-mail asking about the status.