> On Mar 27, 2014, at 3:59 PM, Jesse Gross <je...@nicira.com> wrote: > >> 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.
Maybe the last comment is just redundant, then. Jarno _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
