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

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Date:	Wed, 03 Dec 2008 15:36:29 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Steven Rostedt <rostedt@...dmis.org>
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

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

>> >  # echo $$ > /debugfs/tracing/set_ftrace_pid
>> >  # echo function_graph > /debugfs/tracing/current_tracer
>> > 
>> > Will cause only the current task to be traced. Note, the trace flags are
>> > also inherited by child processes, so the children of the shell
>> > will also be traced.
>> 
>> Where did we end up on the pids-arent-unique issue?  Gave up?
>
> Nah, patch 2 opens the door for a solution. I'm just pawning the work off 
> to the container folks ;-)

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.

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.

Eric
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