linux-kernel - Re: [RFC][PATCH 06/11] sched: Fix trace_sched

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Date:	Tue, 29 Sep 2015 17:48:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, fweisbec@...il.com, oleg@...hat.com,
	umgwanakikbuti@...il.com, tglx@...utronix.de
Subject: Re: [RFC][PATCH 06/11] sched: Fix trace_sched_switch()

On Tue, Sep 29, 2015 at 11:38:12AM -0400, Steven Rostedt wrote:
> On Tue, 29 Sep 2015 11:28:31 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > +static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
> >  {
> > +	return preempt ? TASK_RUNNING | TASK_STATE_MAX : p->state;
> >  }
> 
> Hmm, this original change screwed up kernelshark, as it used the
> state to determine if something was preempted or not. Because now you
> always show a task as running, it can't do that anymore. I think I
> bitched about this before.
> 
> What about nuking the above and just export to the sched_switch
> tracepoint the fact that it was preempted. We now have that information
> passed to it.
> 
> As everything should be using the parsing files, it should not break
> any tools to export it.

/SHOULD/ being the operative word. Experience has taught me that
changing the sched tracepoint leads to borkage.

But we can sure try, see if someone notices etc.. Same with
trace_sched_wakeup(), that still prints a dummy value.
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