linux-kernel - Re: [PATCH:resend] rt: Remove CONFIG_STACK_TRACER from DEBUG

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Message-ID: <z2o520f0cf11004281222h4c1cecb6mf41ab89d66ddfcbf@mail.gmail.com>
Date:	Wed, 28 Apr 2010 21:22:02 +0200
From:	John Kacur <jkacur@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Clark Williams <williams@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH:resend] rt: Remove CONFIG_STACK_TRACER from DEBUG_COUNT, 
	and fix reminder block

On Tue, Apr 27, 2010 at 10:39 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Tue, 27 Apr 2010, John Kacur wrote:
>
>> This fix does two things.
>
> This changelog does suck in more than two ways.
>
>> 1. It reverts commit 3e39399ef4a742d994570488994be93ef17d4ef5.
>> - The above commit added back a warning about CONFIG_STACK_TRACER
>> NOT because the warning was necessary but to fix-up a problem where you could
>> get an empty REMINDER block in the demg.
>
> The CONFIG_STACK_TRACER printk has been there before and got dropped
> for whatever reason, but the DEBUG_COUNT accounting of
> CONFIG_STACK_TRACER still remained.
>
> So the conclusion that the printk needs to be added back is _NOT_
> completely unreasonable.
>
>> However, CONFIG_STACK_TRACER really should not be in the reminder block.
>> Even when configured-in it is not enabled, and thus has neglible impact.
>
> That argument is bogus as it applies to most of the tracing related
> config options.

Not quite. Some of the tracing options are believed to have an impact
even when not enabled.
In particular irqsoff and preemptoff still call a function. Not sure
how minimal the impact is, but
it isn't zero.

>
>> 2. It removes CONFIG_STACK_TRACER from DEBUG_COUNT which is the proper fix
>> for the empty REMINDER block problem.
>
> It's the proper fix if the warning is not justified, which is not
> clear at all. At least not from your changelog.
>
> I do not mind the patch per se, but
>
> 1) the changelog should simply say:
>
>   rt: Remove CONFIG_STACK_TRACER from REMINDER block
>
>   Reason: It does not matter because ....
>
> 2) the patch should cover _all_ tracing options which have no
>   considerable latency impact when just compiled in and not default
>   enabled.
>

Okay, you make some good points, although I'm having a hard time
finding other CONFIGS to safely cut.
Respinning the patch. Thanks for your reply.
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