Re: [PATCH] Replace zone padding with a definition in cache.h

[Nick Piggin]

On Tue, 2005-03-15 at 20:12 -0800, Christoph Lameter wrote:
> This patch removes the zone padding hack and establishes definitions
> in include/linux/cache.h to define the padding within struct zone.
> 
> Signed-off-by: Christoph Lameter <christoph@xxxxxxxxxxx>
> Signed-off-by: Shai Fultheim <Shai@xxxxxxxxxxxx>
> 
> Index: linux-2.6.11/include/linux/cache.h
> ===================================================================
> --- linux-2.6.11.orig/include/linux/cache.h	2005-03-08 18:40:15.000000000 -0800
> +++ linux-2.6.11/include/linux/cache.h	2005-03-14 10:33:45.247701040 -0800
> @@ -48,4 +48,12 @@
>  #endif
>  #endif
> 
> +#ifndef ____cacheline_pad_in_smp
> +#if defined(CONFIG_SMP)
> +#define ____cacheline_pad_in_smp struct { char  x; } ____cacheline_maxaligned_in_smp
                                             ^^^^^^^

Doesn't this add a redundant cacheline if the padding is
previously perfect? Because of the extra byte you're adding?

IIRC, the char x[0]; trick does the job correctly.




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