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

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Message-ID: <alpine.DEB.1.10.0812041653270.32726@gandalf.stny.rr.com>
Date:	Thu, 4 Dec 2008 16:56:28 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
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


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.

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

-- Steve

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