linux-kernel - Re: [PATCH 3/3] ftrace: add ability to only trace swapper tasks

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Date:	Thu, 04 Dec 2008 12:41:08 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	containers@...ts.osdl.org,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 3/3] ftrace: add ability to only trace swapper tasks

Steven Rostedt <rostedt@...dmis.org> writes:

> On Thu, 4 Dec 2008, Eric W. Biederman wrote:
>
>> Ingo Molnar <mingo@...e.hu> writes:
>> 
>> > * Andrew Morton <akpm@...ux-foundation.org> wrote:
>> >
>> >> > Signed-off-by: Steven Rostedt <srostedt@...hat.com>
>> >> 
>> >> What does this patch actually do?  Is swapper currently excluded from 
>> >> tracing for undisclosed reasons and this patch permits it to be traced? 
>> >> If so, why was swapper thus excluded?  Or am I totally off track?
>> >
>> >> > +static struct pid * const ftrace_swapper_pid = (struct pid *)1;
>> >> 
>> >> eh?
>> >
>> > all side-effects of getting rid of the integer based PID namespace and 
>> > replacing them with struct pid pointers.
>> 
>> Thanks for asking Andrew it looks like an unnecessary side effect.
>
> Well, it was necessary without hacking fork.c ;-)

The (struct pid *)1 has always been unnecessary.

As for fork.  It would be nice to remove most of the special cases
for the idle thread.  At least the counts are significant.  The rest
is pretty much a don't care at this point.

Eric

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