Rawhide kernel options not enabled?

Josh Boyer jwboyer at gmail.com
Tue Feb 3 00:55:42 UTC 2009


On Mon, Feb 02, 2009 at 05:34:27PM -0500, Steven Rostedt wrote:
>
>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.

So I'm a kernel dude.  Yet I have to wonder...

What good is that to a normal user?
Why would they ever care about being able to enable function tracing?
Are there shiny GUI tools that do it for them? 
Are there even release notes or wiki pages that tell them how to do it
and why they need it?
If it's that cool, would we ship with it enabled in stable releases?

I can see the value for doing kernel debugging.  Telling a user "do X and
give me the output of Y" could help kernel developers, but the normal user
just isn't going to care.

josh




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