linux-kernel - Re: [PATCH] percpu: fix generic definition of __this_cpu_add_and

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Message-ID: <CAPVoSvSimdFfkxSqtW3Gzf+J-sPPzVuyyUEf7Zxo4HLmBx9kxw@mail.gmail.com>
Date:	Fri, 24 Feb 2012 16:33:48 +0100
From:	Torsten Kaiser <just.for.lkml@...glemail.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: fix generic definition of __this_cpu_add_and_return()

On Sun, Feb 19, 2012 at 3:29 PM, Konstantin Khlebnikov
<khlebnikov@...nvz.org> wrote:
> This patch adds missed "__" into function prefix.
> Otherwise on all archectures (except x86) it expands to irq/preemtion-safe
> variant: _this_cpu_generic_add_return(), which do extra irq-save/irq-restore.
> Optimal generic implementation is __this_cpu_generic_add_return().
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> ---
>  include/linux/percpu.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 32cd1f6..3b609eb 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -718,7 +718,8 @@ do {                                                                        \
>  # ifndef __this_cpu_add_return_8
>  #  define __this_cpu_add_return_8(pcp, val)    __this_cpu_generic_add_return(pcp, val)
>  # endif
> -# define __this_cpu_add_return(pcp, val)       __pcpu_size_call_return2(this_cpu_add_return_, pcp, val)
> +# define __this_cpu_add_return(pcp, val)       \
> +       __pcpu_size_call_return2(__this_cpu_add_return_, pcp, val)
>  #endif
>
>  #define __this_cpu_sub_return(pcp, val)        this_cpu_add_return(pcp, -(val))

I think, the same fix should be applied to the lines following this patch:
#define __this_cpu_sub_return(pcp, val) this_cpu_add_return(pcp, -(val))
#define __this_cpu_inc_return(pcp)      this_cpu_add_return(pcp, 1)
#define __this_cpu_dec_return(pcp)      this_cpu_add_return(pcp, -1)

Shouldn't these other operations also only give the __ relaxed guarantees?

HTH

Torsten
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