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

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Message-ID: <alpine.DEB.1.10.0812041551590.32726@gandalf.stny.rr.com>
Date:	Thu, 4 Dec 2008 15:57:48 -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:
> >> >
> >> >> > +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.

Well, I could set it to the &init_struct_pid as you said, but it will not 
change any of the code below it. So it does not matter what 
ftrace_swapper_pid is set to, as long as it is not set to something that 
can be a legitimate pid struct for something not the swapper task.

It will only matter when we fix the fork code.

> 
> 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.

Well, the swapper task should still have a pid of zero. That is probably 
important.

-- Steve

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