[PATCH 0/3] ARM Coresight: Enhance ETM tracing control

[Adrien Vergé]

2013/12/4 Greg Kroah-Hartman <gregkh at linuxfoundation.org>:
> How much overhead does the existing tracing code have on ARM?  Is ETM
> still even needed?  Why not just use ETM for the core tracing code
> instead?

Coresight ETM is not just faster than /sys/kernel/debug/tracing, it
provides more detailed and customisable info. For instance, you can
trace every load, store, instruction fetch, along with the number of
cycles taken, with almost zero-overhead.

> What's wrong with the in-kernel tracing logic that you can't use that
> instead of the ETM stuff?

ETM has a different purpose. Integrating it in
/sys/kernel/debug/tracing would not take advantage of all its
features.