linux-kernel - Re: [PATCH 3/3] ftrace: trace single pid for function graph tracer

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Message-ID: <alpine.DEB.1.10.0812032125340.28153@gandalf.stny.rr.com>
Date:	Wed, 3 Dec 2008 21:29:10 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com,
	peterz@...radead.org, arjan@...radead.org, dave@...ux.vnet.ibm.com,
	containers@...ts.osdl.org, sukadev@...ux.vnet.ibm.com,
	serue@...ibm.com, srostedt@...hat.com
Subject: Re: [PATCH 3/3] ftrace: trace single pid for function graph tracer

On Wed, 3 Dec 2008, Eric W. Biederman wrote:

> Steven Rostedt <rostedt@...dmis.org> writes:
> 
> The way patch 2 uses pids is just stupid.  It has nothing to do with
> pids aren't unique.  You do a full walk of the process list instead
> of using the hash table.

The way patch 2 uses the pids is stupid, it was just the easiest way to 
implement it correctly ;-)  I work with, do it stupid but correct first, 
then optimize.

> 
> It makes me think that task->pid really should go away because with it
> there people don't bother to look and see how things normally work.

This is far from a fast path, and I can easily fix it. The hard work was 
the rest of the patch not this part. I even did it stupid knowing that I 
would be rewriting it to handle namespaces. I stated that this needed to 
be fixed in the patch itself.

One thing I never got an answer for, using the namespace pid path, can I 
still select the idle task to trace, i.e. pid == 0.

-- Steve

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