linux-kernel - Re: [PATCH] mn10300: select generic atomic64

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Date:	Fri, 28 Dec 2012 23:15:23 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Fengguang Wu <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-am33-list@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mn10300: select generic atomic64_t support

On Tue, Aug 14, 2012 at 5:17 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> Rationals from Eric:
>
> So I just looked a little deeper and it appears architectures that do
> not support atomic64_t are broken.
>
> The generic atomic64 support came in 2009 to support the perf subsystem
> with the expectation that all architectures would implement atomic64
> support.
>
> Furthermore upon inspection of the kernel atomic64_t is used in a fair
> number of places beyond the performance counters:
>
> block/blk-cgroup.c
> drivers/acpi/apei/
> drivers/block/rbd.c
> drivers/crypto/nx/nx.h
> drivers/gpu/drm/radeon/radeon.h
> drivers/infiniband/hw/ipath/
> drivers/infiniband/hw/qib/
> drivers/staging/octeon/
> fs/xfs/
> include/linux/perf_event.h
> include/net/netfilter/nf_conntrack_acct.h
> kernel/events/
> kernel/trace/
> net/mac80211/key.h
> net/rds/
>
> The block control group, infiniband, xfs, crypto, 802.11, netfilter.
> Nothing quite so fundamental as fs/namespace.c but definitely in
> multiplatform-code that should work, and is already broken on those
> architecutres.
>
> Looking at the implementation of atomic64_add_return in lib/atomic64.c
> the code looks as efficient as these kinds of things get.
>
> Which leads me to the conclusion that we need atomic64 support on all
> architectures.
>
> CC: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>

Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

> ---
>  arch/mn10300/Kconfig |    1 +
>  1 file changed, 1 insertion(+)
>
> --- linux.orig/arch/mn10300/Kconfig     2012-08-03 15:36:21.391560778 +0800
> +++ linux/arch/mn10300/Kconfig  2012-08-14 22:53:14.751795832 +0800
> @@ -8,6 +8,7 @@ config MN10300
>         select HAVE_ARCH_KGDB
>         select HAVE_NMI_WATCHDOG if MN10300_WD_TIMER
>         select GENERIC_CLOCKEVENTS
> +       select GENERIC_ATOMIC64
>
>  config AM33_2
>         def_bool n

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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