linux-kernel - Re: [RFC][PATCH] tracing/module: Move tracepoint out of module.h

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Date:	Thu, 26 Jan 2012 09:04:29 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [RFC][PATCH] tracing/module: Move tracepoint out of module.h

[ Added Li who added the original tracepoint ]

On Thu, 2012-01-26 at 14:55 +0100, Ingo Molnar wrote:
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Thu, 2012-01-26 at 11:28 +0100, Ingo Molnar wrote:
> > 
> > > How much more do we save if we move all of try_module_get() out 
> > > of line? It still seems a rather thick inline function with 
> > > preempt section and all. I'd *really* suggest that it should all 
> > > be uninlined.
> > > 
> > 
> > Here's the #'s
> > 
> >    text	   data	    bss	    dec	    hex	filename
> > 7489488	2249584	9719808	19458880	128eb40	vmlinux-prepatch
> >    text	   data	    bss	    dec	    hex	filename
> > 7482458	2248048	9719808	19450314	128c9ca	vmlinux-postpatch
> >    text	   data	    bss	    dec	    hex	filename
> > 7477393	2248080	9719808	19445281	128b621	vmlinux-updatedpatch
> > 
> > Thus we get an additional 5k it seems, for a total of 13k savings.
> > 
> > The below patch is what I used. Note, since the tracepoint 
> > requires the instruction pointer, I created stub versions that 
> > call a "do_" version of the function to pass in the local 
> > instruction counter.
> 
> Hm, why does this tracepoint include a flat RIP? It's pretty 
> superfluous as there's various other (orghogonal) ways to get at 
> the RIP.
> 
> If the field is needed for compatibility then lets set it to 
> zero at the tracepoint level and not burden the module.h 
> hotpath.

Perhaps I could use "__builtin_return_address(0)" instead. I'll try that
out. That way, we don't burden the module hotpath, and we keep the old
behavior.

-- Steve


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