On Tue, Jun 02, 2015 at 07:58:48AM -0700, Ben Pfaff wrote: > On Mon, Jun 01, 2015 at 03:35:23PM -0700, Jesse Gross wrote: > > On Mon, Jun 1, 2015 at 2:55 PM, Ben Pfaff <b...@nicira.com> wrote: > > > On Mon, Jun 01, 2015 at 01:49:30PM -0700, Jesse Gross wrote: > > >> We have a special flow_metadata structure to represent the parts > > >> of a packet that aren't carried in the payload itself. This is > > >> used in the case where we need to send the packet as a Packet In > > >> to an OpenFlow controller. This is a subset of the more general > > >> struct flow. > > >> > > >> In practice, almost all operations we do on this structure involve > > >> converting it to or from a match or have code that is the same as > > >> a match. Serialization to NXM and back is done as a match. There > > >> is special flow_metadata formatting code that is almost identical > > >> to match formatting. > > >> > > >> The uses for struct flow_metadata aren't performance critical > > >> when it comes to memory, so we can save quite a bit of code by > > >> just using a match structure directly instead. In addition, as > > >> metadata increases and becomes more complex (Geneve options require > > >> some special handling beyond just additional fields), using the > > >> match structure means we only have to do this work in one place. > > >> > > >> Signed-off-by: Jesse Gross <je...@nicira.com> > > > > > > Most of this rationale makes sense to me, except that I'm surprised > > > that struct flow_metadata (which doesn't have masks) gets converted to > > > struct match (which does). Maybe I should just dig into the code, but > > > is there some big reason why this is the case? > > > > The main reason is just that struct match is the more general superset > > and the encode/decoding/formatting code operates on that to be able to > > handle everything so it's cleaner to just use a match even if it is > > slightly less memory efficient. > > It just seems conceptually wrong to me to have masks around in cases > where there's no concept of one, where the masks just take up space and > get ignored. I'm trying to figure out how much that bothers me.
So, I guess, the summary of my thoughts about this right now is that for me it's a no-brainer to switch from a specialized structure to struct flow, but struct match is a little harder for me conceptually. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
