linux-kernel - Re: [PATCH 0/4] jump label patches

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Message-ID: <4ACCB52D.3020104@redhat.com>
Date:	Wed, 07 Oct 2009 08:35:09 -0700
From:	Richard Henderson <rth@...hat.com>
To:	Roland McGrath <roland@...hat.com>
CC:	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, mathieu.desnoyers@...ymtl.ca, tglx@...utronix.de,
	rostedt@...dmis.org, ak@...e.de, mhiramat@...hat.com
Subject: Re: [PATCH 0/4] jump label patches

On 10/06/2009 05:14 PM, Roland McGrath wrote:
> Kernel builds usually use -Os.  Is there anything else we can do now (4.4)
> to influence this placement (while keeping the unlikely target block inside
> a scope, i.e. macro, with the asm goto)?

I think -Os includes -freorder-blocks as well.

> 	      if (0) yes: maybe = 1;

Anything with "if (0)" in it (even with __builtin_expect) is going to be 
folded away too early to be useful.

I can't think of any way to manipulate block placement from the source 
level at this time that doesn't add more code along the fast path, 
obviating the asm goto.


r~
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