Re: [PATCH v2 net-next af-packet 1/2] Enhance af-packet to provide (near zero)lossless packet capture functionality.

From: chetan loke <redacted>
Date: Wed, 6 Jul 2011 17:45:20 -0400

new format:

union bd_header_u {
       /* renamed struct bd_v1 to hdr_v1 */
       struct hdr_v1 h1;
} __attribute__ ((__packed__));

struct block_desc {
       __u16 version;
       __u16 offset_to_priv;
       union bd_header_u hdr;
} __attribute__ ((__packed__));

Is this ok with you?

Get rid of __packed__, it's going to kill performance on RISC
platforms.  If you use __packed__, regardless of the actual alignment,
the compiler must assume that each part of the struct "might" be
unaligned.  So on architectures such as sparc where alignment matters,
a word is going to be accessed by a sequence of byte loads/stores.

Do not use packed unless absolutely enforced by a protocol or hardware
data structure, it's evil.