linux-kernel - Re: Kernel marker has no performance impact on ia64.

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Message-ID: <20080612174834.GB22454@redhat.com>
Date:	Thu, 12 Jun 2008 13:48:34 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Hideo AOKI <haoki@...hat.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: Kernel marker has no performance impact on ia64.

Hi -

On Thu, Jun 12, 2008 at 01:05:52PM -0400, Masami Hiramatsu wrote:
> [...]
> >> "sched_switch(struct task_struct * next, struct task_struct * prev)":"next %p prev %p"
> >> out of tree. Thus, you can use the printf-style format parser.
> > 
> > That's an interesting idea, but errors in this table would themselves
> > only be caught at C compilation time.

> Hmm, why would you think so?  I think if we can't find corresponding
> entry from the lookup table, it becomes an error.

Sure, but if the entry exists but is wrong, we'd emit C code that
won't compile.


> [...] Even if you use trace_mark() markers, you have to post a
> kernel patch which passes the prev->pid to the marking point and to
> discuss it.  for example,
> DEFINE_TRACE(sched_switch, (int prev_pid, int next_pid), prev_pid, next_pid)

(If it were up to me, I would add the task pointers too, which
debuginfo-less systemtap could ignore but other tracers may use.)


> But it might not so general, we have to discuss what parameters are
> enough good for each marking point.

That's exactly what the "lttng instrumentation markers" threads from
the recent past had started.


- FChE
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