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Subject: RE: [PATCH] acpi: remove function tracing macros
Date: Mon, 16 Jan 2006 15:01:46 -0500
Message-ID: <F7DC2337C7631D4386A2DF6E8FB22B3005B8388F@hdsmsx401.amr.corp.intel.com>
Thread-Topic: [PATCH] acpi: remove function tracing macros
Thread-Index: AcYazTugRYK0jp1nRH2pxWFu3EZoDQACOcgg
From: "Brown, Len" <len.brown@intel.com>
To: "Pekka Enberg" <penberg@cs.helsinki.fi>
Cc: <linux-acpi@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2495
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>I appreciate that but per-function tracing is overkill.

I agree that 100% function coverage is overkill.
However, 100% is preferable to 0%.
The most desirable middle-ground will take some work
on the part of the folks that actually use the tracing.

>Especially since
>the macros used for it are very obfuscating (i.e. return_VALUE, et al)
>and we have things like kprobes.

Everybody agreees with you about the return_VALUE syntax.
The other irritating thing about this instrumentation is
that the function trace header looks like a call, but
is actually a declaration -- so sometimes DEBUG builds
break when executable code is put before it.  The fortunate
thing is that a relatively small group of people make
changes to the ACPI sub-system and this is one of the
things they learn about quickly:-)

If kprobes can give us the same functionality,
I'll be delighted if somebody can show me how.

>On Mon, 2006-01-16 at 13:14 -0500, Brown, Len wrote:
>> When we make GPL changes to those files, we diverge
>> from the rest of the universe and the overloaded
>> Linux/ACPI maintainer (me) starts to lose his sanity.
>> That said, if the author of the patch re-licenses it back
>> to Intel so it can be distributed under eitiher GPL or BSD,
>> then Intel can apply a change "up-stream" and divergence
>> can be avoided.  But per above, that isn't the primary
>> issue with ripping out tracing.
>> 
>> Note that tracing is built in only for CONFIG_ACPI_DEBUG.
>
>My main concern is that the ACPI subsystem uses obfuscating macros to
>implement function tracing in the kernel. Please note that we do not
>allow this in new code and there are janitor such as myself that are
>working to remove the existing ones.
>
>While I have no intention of making your life as Linux maintainer
>harder, I would appreciate if you would at least consider ripping out
>function tracing from upstream. I am certainly willing to relicense or
>even transfer copyrights of the patch if that's what you need.

I share your concern about source code style.
Note that as I mentioned, we've got some changes in the pipeline
to clean up drivers/acpi/*.c already.
Changing this in the upstream interpreter in drivers/acpi/*/
will be harder and will take longer.

thanks,
-Len
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