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List:       user-mode-linux-devel
Subject:    Re: [uml-devel] [PATCH 6/6] Add support for __read_mostly to
From:       Christoph Lameter <cl () linux ! com>
Date:       2009-05-01 13:52:18
Message-ID: alpine.DEB.1.10.0905010948140.18324 () qirst ! com
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On Fri, 1 May 2009, Sam Ravnborg wrote:

> Are there any specific reason why we do not support read_mostly on all
> architectures?

Not that I know of.

> read_mostly is about grouping rarely written data together
> so what is needed is to introduce this section in the remaining
> archtectures.
>
> Christoph - git log says you did the inital implmentation.
> Do you agree?

Yes.

There is some concern that __read_mostly is needlessly applied to
numerous variables that are not used in hot code paths. This may make
__read_mostly ineffective and actually increase the cache footprint of a
function since global variables are no longer in the same cacheline. If
such a function is called and the caches are cold then two cacheline
fetches have to be done instead of one.



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