Re: [iptables PATCH] list: fix prefetch dummy

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 06 Apr 2015 20:05:41 +0200
Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com> wrote:

> linux_list.h:381:59: warning: right-hand operand of comma expression has no effect [-Wunused-value]
>   for (pos = list_entry((head)->next, typeof(*pos), member), \
>                                                            ^
> libiptc.c:552:2: note: in expansion of macro 'list_for_each_entry'
>   list_for_each_entry(c, &h->chains, list) {
>   ^
> 
> [ Patch copied from one similar of Patrick McHardy on libnftnl ]
> 
> Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
> ---
>  libiptc/linux_list.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libiptc/linux_list.h b/libiptc/linux_list.h
> index abdcf88..559e33c 100644
> --- a/libiptc/linux_list.h
> +++ b/libiptc/linux_list.h
> @@ -27,7 +27,7 @@
>  	1; \
>  })
>  
> -#define prefetch(x)		1
> +#define prefetch(x)		((void)0)
>  
>  /* empty define to make this work in userspace -HW */
>  #define smp_wmb()
> 
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The kernel dropped the prefetch() in the list macros a couple
of years ago. The prefetch() had no performance gain and hurt
in several cases.