On Wed, Jul 14, 2021 at 11:20:00AM +0000, Keller, Jacob E wrote: > I think for Tx the challenges are higher: the timestamp is taken > after we've filled in the descriptor and sent the frame. The only > place it could reasonably be stored again is the descriptor > writeback (since we don't get completion messages).
Right, the would be the place to do it. > If I remember correctly, the challenge here is that in a traditional > ring model the writeback is completed much earlier than the > timestamp so we potentially delay cleanup of other packets by > waiting to insert the timestamp into the writeback. If *every* frame gets a time stamp, then their write-backs would all be delayed by the same amount. Hence no clean up operations would be "delayed". They would all take the same amount of time. The only cost would be in space to keep the data for the write-back around until the time stamp becomes available. Paying the price of the little extra memory is well worth it, as it simplifies the time stamping logic and removes every class of problem related to time stamp delivery. IOW, KISS! Thanks, Richard _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
