On Fri, Feb 21, 2014 at 11:41 AM, Jarno Rajahalme <jrajaha...@nicira.com> wrote: > Minimize padding in sw_flow_key and move 'tp' top the main struct. > These changes simplify code when accessing the transport port numbers > and the tcp flags, and makes the sw_flow_key 8 bytes smaller on 64-bit > systems (128->120 bytes). These changes also make the keys for IPv4 > packets to fit in one cache line. > > There is a valid concern for safety of packing the struct > ovs_key_ipv4_tunnel, as it would be possible to take the address of > the tun_id member as a __be64 * which could result in unaligned access > in some systems. However: > > - sw_flow_key itself is 64-bit aligned, so the tun_id within is always > 64-bit aligned. > - We never make arrays of ovs_key_ipv4_tunnel (which would force every > second tun_key to be misaligned). > - We never take the address of the tun_id in to a __be64 *. > - Whereever we use struct ovs_key_ipv4_tunnel outside the sw_flow_key, > it is in stack (on tunnel input functions), where compiler has full > control of the alignment.
I'm not sure that I understand the last comment here. On the stack, the compiler does have control over the layout but it will presumably use the alignment specified here when doing that layout. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
