linux-kernel - Re: [PATCH 09/15] xen/trace: add tlb flush tracepoints

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Date:	Thu, 23 Jun 2011 22:00:01 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Xen Devel <Xen-devel@...ts.xensource.com>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 09/15] xen/trace: add tlb flush tracepoints

On Thu, 2011-06-23 at 15:58 -0700, Jeremy Fitzhardinge wrote:

> > If you really need something like this, maybe I'll add a
> > DEFINE_EVENT_NOARGS() that will not require arguments and can eliminate
> > a lot of code that TRACE_EVENT() adds.
> 
> If you like, but only if you think its worth the effort.  The empty
> string thing is a bit of an ugly hack, but its not like it makes a mess
> everywhere.

The problem I have is not the ugliness, but more of the wasted code that
is generated to do nothing. The TRACE_EVENT() generates lots of helper
functions that are unique to handle different events. The fact that we
have no args is generating code that does a lot of nothing. Every
TRACE_EVENT() can create 5k of code/data. This is why I advocate the
DEFINE_TRACE_CLASS() and DEFINE_EVENT() because it reuses a lot of the
code.

If we had a NOARGS event that was just a marker, then we could eliminate
most of the helper functions for these kinds of trace points.

-- Steve

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