From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Kyle McMartin <kyle@mcmartin.ca>, Adrian Bunk <bunk@kernel.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: RFC: remove __read_mostly
Date: Mon, 17 Dec 2007 02:33:39 -0800 [thread overview]
Message-ID: <20071217023339.ce3da56c.akpm@linux-foundation.org> (raw)
In-Reply-To: <p73tzmmf72u.fsf@bingen.suse.de>
On Fri, 14 Dec 2007 01:33:45 +0100 Andi Kleen <andi@firstfloor.org> wrote:
> Kyle McMartin <kyle@mcmartin.ca> 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.
next prev parent reply other threads:[~2007-12-17 10:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-13 22:20 RFC: remove __read_mostly Adrian Bunk
2007-12-13 22:29 ` Andi Kleen
2007-12-13 22:41 ` Adrian Bunk
2007-12-14 16:16 ` Arnd Bergmann
2007-12-14 16:31 ` Eric Dumazet
2007-12-13 22:32 ` David Miller
2007-12-13 22:44 ` Harvey Harrison
2007-12-13 23:06 ` Andi Kleen
2007-12-13 22:48 ` Eric Dumazet
2007-12-13 23:00 ` Adrian Bunk
2007-12-13 23:54 ` Kyle McMartin
2007-12-14 0:33 ` Andi Kleen
2007-12-17 10:33 ` Andrew Morton [this message]
2007-12-17 10:53 ` Eric Dumazet
2007-12-17 11:07 ` Andrew Morton
2007-12-17 12:19 ` Andi Kleen
2007-12-17 12:15 ` Andi Kleen
2007-12-17 12:40 ` Adrian Bunk
2007-12-14 15:24 ` Matt Mackall
2007-12-14 15:38 ` Eric Dumazet
2007-12-14 15:42 ` Matt Mackall
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