|| ||Andrew Morton <akpm-AT-linux-foundation.org>|
|| ||Andi Kleen <andi-AT-firstfloor.org>|
|| ||Re: RFC: remove __read_mostly|
|| ||Mon, 17 Dec 2007 02:33:39 -0800|
|| ||Kyle McMartin <kyle-AT-mcmartin.ca>, Adrian Bunk <bunk-AT-kernel.org>,
On Fri, 14 Dec 2007 01:33:45 +0100 Andi Kleen <email@example.com> wrote:
> Kyle McMartin <firstname.lastname@example.org> writes:
> > I'd bet, in the __read_mostly case at least, that there's no
> > improvement in almost all cases.
> I bet you're wrong. Cache line behaviour is critical, much more
> than pipeline behaviour (which unlikely affects). That is because
> if you eat a cache miss it gets really expensive, which e.g.
> a mispredicted jump is relatively cheap in comparison. We're talking
> one or more orders of magnitude.
So... once we've moved all read-mostly variables into __read_mostly, what
is left behind in bss?
All the write-often variables. All optimally packed together to nicely
maximise cacheline sharing.
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