linux-kernel - Re: [PATCH 03/13] jump label v9: x86 support

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Message-ID: <20100610142825.GB19561@basil.fritz.box>
Date:	Thu, 10 Jun 2010 16:28:25 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	rostedt@...dmis.org, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com, avi@...hat.com,
	davem@...emloft.net, vgoyal@...hat.com, sam@...nborg.org
Subject: Re: [PATCH 03/13] jump label v9: x86 support

On Thu, Jun 10, 2010 at 04:12:11PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-06-10 at 15:26 +0200, Andi Kleen wrote:
> > The code generated by -Os is often terrible.
> 
> Is anybody on the gcc side of things looking into curing that?

The problem is that the smallest code is often terrible.
You could often be much better with spending a few more bytes.
But -Os means "smallest"

On the other hand -Os could be likely made smaller
(it often still is not very good), but I fear that would
make things even worse.

We probably would need a -Osmall-but-not-terrible or so,
but that's not there. 
> 
> I mean, what's the point of having an -Os if its useless in practise.

I think __hot / __cold but keeping the default at -O2 is a better
approach anyways. Hot paths should be -O2.  It just needs some more work.

It already works for __init/__exit at least.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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