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

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Date:	Thu, 04 Dec 2008 23:43:52 -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:
>> 
>> Right.  I simply meant most of the
>> if (likely(p->pid)) conditional except for the counts is pretty much a don't
>> care.  Keeping the idle tasks off of the process list and out of the counts
>> is useful.
>> 
>> For this particular case what problem did you see with calling attach_pid
>> with PIDTYPE_PID on init_struct_pid?
>
> On boot up, the CPU 0 idle task is attached to init_struct_pid, and not 
> the others. If you do a "attach_pid" on the next idle task that is created, 
> it will become the attched process, bumping off CPU 0's idle task from the 
> init_struct_pid.

It should form a linked list.  For other pid types we don't have a problem.

> When doing the code you suggested, I end up with only marking the last 
> idle task to be created.

Odd. It is all a linked list through the task structures.
I'm guessing the initialization isn't quite right.

Weird.  

Eric






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