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[microblaze-uclinux] Re: [PATCH 6/6] Add support for __read_mostly to linux/cache.h
- To: Sam Ravnborg <sam@xxxxxxxxxxxx>
- Subject: [microblaze-uclinux] Re: [PATCH 6/6] Add support for __read_mostly to linux/cache.h
- From: Christoph Lameter <cl@xxxxxxxxx>
- Date: Fri, 1 May 2009 09:52:18 -0400 (EDT)
- Cc: Tim Abbott <tabbott@xxxxxxx>, Anders Kaseorg <andersk@xxxxxxx>, Waseem Daher <wdaher@xxxxxxx>, Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx>, Jeff Arnold <jbarnold@xxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Bryan Wu <cooloney@xxxxxxxxxx>, Chris Zankel <chris@xxxxxxxxxx>, Cyrill Gorcunov <gorcunov@xxxxxxxxxx>, David Howells <dhowells@xxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, dev-etrax@xxxxxxxx, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>, Greg Ungerer <gerg@xxxxxxxxxxx>, Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>, Heiko Carstens <heiko.carstens@xxxxxxxxxx>, Helge Deller <deller@xxxxxx>, Hirokazu Takata <takata@xxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Jeff Dike <jdike@xxxxxxxxxxx>, Jesper Nilsson <jesper.nilsson@xxxxxxxx>, Kyle McMartin <kyle@xxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, linux-alpha@xxxxxxxxxxxxxxx, linux-am33-list@xxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-m32r@xxxxxxxxxxxxxxxxx, linux-m68k@xxxxxxxxxxxxxxx, linux-mips@xxxxxxxxxxxxxx, linux-parisc@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, Martin Schwidefsky <schwidefsky@xxxxxxxxxx>, Michal Simek <monstr@xxxxxxxxx>, microblaze-uclinux@xxxxxxxxxxxxxx, Mikael Starvik <starvik@xxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, Paul Mundt <lethal@xxxxxxxxxxxx>, Ralf Baechle <ralf@xxxxxxxxxxxxxx>, Richard Henderson <rth@xxxxxxxxxxx>, Roman Zippel <zippel@xxxxxxxxxxxxxx>, Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>, sparclinux@xxxxxxxxxxxxxxx, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, uclinux-dist-devel@xxxxxxxxxxxxxxxxxxxx, user-mode-linux-devel@xxxxxxxxxxxxxxxxxxxxx, Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
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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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