linux-kernel - Re: [RFT][patch 17/18] sched: use jump labels to reduce overhead when bandwidth control is inactive

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Message-ID: <1312557254.28695.12.camel@twins>
Date:	Fri, 05 Aug 2011 17:14:14 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Richard Henderson <rth@...hat.com>
Cc:	Jason Baron <jbaron@...hat.com>, Paul Turner <pjt@...gle.com>,
	linux-kernel@...r.kernel.org,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <bsingharora@...il.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFT][patch 17/18] sched: use jump labels to reduce overhead
 when bandwidth control is inactive

On Fri, 2011-08-05 at 08:11 -0700, Richard Henderson wrote:
> On 08/05/2011 01:30 AM, Peter Zijlstra wrote:
> > OK, so _WHY_ does that make a difference and will a next version of
> > gnu-binutils not mess that up?
> 
> The Why is micro-architectual, and I can't answer that.
> 
> But ld will never re-order the files as given on the command-line.
> There are too many functions and tables that are constructed 
> piece-wise from input sections; re-ordering them would change
> the semantics of the program.

Right, so I was wondering about things like whole-program-optimization
passes at link time. Since I've no clue why the proposed patch does what
it does, its hard to say what invariant is needed to be kept.


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