linux-kernel - Re: [PATCH 09/11] sched: export task

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Date:	Thu, 1 Dec 2011 17:15:00 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Greg KH <greg@...ah.com>, devel@...verdev.osuosl.org,
	lttng-dev@...ts.lttng.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Darren Hart <darren@...art.com>
Subject: Re: [PATCH 09/11] sched: export task_prio to GPL modules

* Peter Zijlstra (peterz@...radead.org) wrote:
> On Thu, 2011-12-01 at 17:04 -0500, Mathieu Desnoyers wrote:
> > * Peter Zijlstra (peterz@...radead.org) wrote:
> > > On Thu, 2011-12-01 at 16:41 -0500, Mathieu Desnoyers wrote:
> > > > LTTng needs this symbol to prepend the current task dynamic priority
> > > > value to events (optional context information).
> > > 
> > > I absolutely detest exporting such stuff. It propagates the idea that
> > > task prio actually means something. Also, modules really shouldn't care.
> > 
> > People debugging their SCHED_FIFO/SCHED_RR applications, as well as
> > users of priority-inheritance futexes, may happen to find this
> > information extremely useful.
> > 
> > Just saying...
> 
> Right until the moment we go do deadlines.. Anyway, it still doesn't
> make sense, your sched_switch() tracepoint handler gets this
> information, why do you need this export at all?

If you don't want to trace sched_switch, but just conveniently prepend
this information to all your events, then lttng lets you dynamically
target this extra bit of information. Note that it's not a mandatory
event field: I call those "context" fields that the tracer prepends to
events, as requested by the user.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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