linux-kernel - Re: [PATCH] ftrace: Remove use of control list and ops

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Message-ID: <20151201155744.GA24786@krava.local>
Date:	Tue, 1 Dec 2015 16:57:44 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] ftrace: Remove use of control list and ops

On Tue, Dec 01, 2015 at 09:55:54AM -0500, Steven Rostedt wrote:
> On Tue, 1 Dec 2015 14:42:36 +0100
> Jiri Olsa <jolsa@...hat.com> wrote:
> 
> > On Mon, Nov 30, 2015 at 05:36:40PM -0500, Steven Rostedt wrote:
> > > 
> > > [ Jiri, can you take a look at this. You can also apply it on top of my
> > >   branch ftrace/core, and run any specific tests. I just need to nuke
> > >   that control structure for further updates with ftrace. ]
> > > 
> > > 
> > > Currently perf has its own list function within the ftrace infrastructure
> > > that seems to be used only to allow for it to have per-cpu disabling as well
> > > as a check to make sure that it's not called while RCU is not watching. It
> > > uses something called the "control_ops" which is used to iterate over ops
> > > under it with the control_list_func().
> > > 
> > > The problem is that this control_ops and control_list_func unnecessarily
> > > complicates the code. By replacing FTRACE_OPS_FL_CONTROL with two new flags
> > > (FTRACE_OPS_FL_RCU and FTRACE_OPS_FL_PER_CPU) we can remove all the code
> > > that is special with the control ops and add the needed checks within the
> > > generic ftrace_list_func().  
> > 
> > hum,
> > do we need also change for the trampoline, something like below?
> > 
> > I needed attached patch to get the perf ftrace:function
> > event work properly..
> 
> Hmm, I thought that I forced the list function when RCU or PER_CPU
> was set. Oh wait. I have CONFIG_PREEMPT set, which will change the
> logic slightly. I'm guessing you have PREEMPT_VOLUNTARY set. I'll try
> that out.

yep, but the trampoline has separate code path
to set the ops func

jirka
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