linux-kernel - Re: RFC: remove __read

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Message-ID: <20071213235432.GA26669@fattire.cabal.ca>
Date:	Thu, 13 Dec 2007 18:54:32 -0500
From:	Kyle McMartin <kyle@...artin.ca>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: RFC: remove __read_mostly

On Thu, Dec 13, 2007 at 11:20:44PM +0100, Adrian Bunk wrote:
> Is there anywhere in the kernel a case where __read_mostly brings a 
> measurable improvement or can it be removed?
> 

Yes, definitely[1]... the problem is, and this is also true of other
annotations[2], that people go absolutely nuts adding these annotations
without doing any profiling to see whether they actually improve things.

I'd bet, in the __read_mostly case at least, that there's no
improvement in almost all cases.

cheers, Kyle

1. It's hugely relevant on big-SMP machines.
2. I mean __read_mostly, likely, unlikely, etc., not the useful sparse
annotations.
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