Vareka, Bill wrote: > Here is a patch to add the option of joint slots. I have not had a chance to > fully test this but the changes are fairly confined so this should be good. >
Great work, and also very well described. Thanks for your contribution! > The basic idea is that you define multiple slots but all but the first are > defined as 'joined' to the first one. Then when you write via the socket, > the data goes to a common slot buffer and is sent in the next assigned slot. > This can be used to significantly reduce latencies without requiring very > short cycle periods. > > The changes are: > 1) add a -j option to tdmacfg for 'slots' which takes the joint slot id. It > will be required that the slot you want to reference to must have already > been defined before you define the joint slot. Also, the mtu's of both > the slot your joining and your own slot must be the same. > > 2) The tdma_config struct adds an additional int field called jointslot to > the set_slot union. A value between 0 and MaxSlots indicates a > desire to be coupled. Default is -1 (no coupling). > > 3) Modify the tdma_slot by changing the 'queue' member to be a pointer to a > rtskb_prio_queue and add an additional actual rtskb_prio_queue called > myqueue. > > 4) By default, slot->queue just points to &slot->myqueue. > > 5) The act of joining is achieved by changing slot->queue to point to > another pre-existing slot's myqueue member. > > 6) the rest of the tdma_slot structs for the two joint slots are not > identical because this is where things like offset, period and phasing info > are kept and those are different for the two slots. Only the > rtskb_prio_queue is common between them. > > 7) If you remove a slot which is jointed to another slot but you're not the > reference, then you just delete normally. But if others have queue pointer > pointing to your myqueue object then all those slots have their queue's > redirected to their own myqueue objects. Obviously, care is taken that this > is done when ref_count is 0 so we don't corrupt a loop in progress. > > 8) The only other impact is a few function calls which currently have > &slot->queue which needed to be changed to slot->queue since it's a pointer > already. Looks good. On the first glace I had some concerns regarding the loops over all slots under spinlock to find potential mates (even when there are none), but I see no other simple solution so far. Will try to think about it further, though. > > 9) An unrelated bug was addressed, in the original tdma_ioctl.c file on line > 474 the original code had > while ((rtskb = __rtskb_prio_dequeue(&slot->queue))) > but I believe the correct call should have been > while ((rtskb = __rtskb_prio_dequeue(&old_slot->queue))) > I've incorporated that into this patch as well but it is really independent > of the joint-slots changes. Oh, yes, good spot. Looks like some real cleanup bug... > > Unlike what I stated in an earlier post, this no longer treats the NRT slot > any different from the others, thus you can also join to it if you want. > Ok, I have some code refactoring still pending on my box which I would like to finish and check in first, but then it will be your patch's turn. Should definitely make it into SVN for the next release! Jan
signature.asc
Description: OpenPGP digital signature
