netdev - [RFC] change dst_entry padding from using an array to using __attribute_

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Message-ID: <t2o97949e3e1004070946mfacef7c0la6bddc38d29720ae@mail.gmail.com>
Date:	Wed, 7 Apr 2010 09:46:28 -0700
From:	Laurent Chavey <chavey@...gle.com>
To:	netdev@...r.kernel.org
Cc:	laurent chavey <chavey@...gle.com>
Subject: [RFC] change dst_entry padding from using an array to using 
	__attribute__

what are the benefit(s)  of using an array to force a struct
element to be aligned on 64 bytes / 32 bytes boundaries
versus using gcc __attribute__.


------------------------------------

struct dst_entry {

       /*
        * Align __refcnt to a 64 bytes alignment
        * (L1_CACHE_SIZE would be too much)
        */
- #ifdef CONFIG_64BIT
-       long                    __pad_to_align_refcnt[1];
- #else
-       long                    __pad_to_align_refcnt[0];
- #endif
+       atomic_t                __refcnt __attribute__
((aligned(64))); /* client references    */
#undef __padding__
       /*
        * __refcnt wants to be on a different cache line from
        * input/output/ops or performance tanks badly
        */
       atomic_t                __refcnt;       /* client references    */
};
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