On Mon, 2 Feb 2009, Roland McGrath wrote:
> I thought we were going to enable these in rawhide since the
e1000
> EEPROM problem was fixed:
>
> CONFIG_FUNCTION_TRACER (was CONFIG_FTRACE)
> CONFIG_DYNAMIC_FTRACE
Last I knew this still uses -pg and implies -fno-omit-frame-pointer.
This probably kills performance somewhat, and more importantly during a
rawhide debug-kernel phase, might change the corners of compiler behavior
that we're checking vs what we'd want in a production kernel.
The performance hit by -fno-omit-frame-pointer depends on the which
hardware you are running. I've been told by Arjan that the latest x86
hardware has negligible performance hit on this feature.
But with this on, you can enable kernel function tracing at runtime. And
this is a very powerful tool. This might be something to discuss, where we
may sacrifice a bit of power for the ability of dynamic tracing.
Benchmarks welcome ;-)
-- Steve