We wanted to handle 10's K of VoIP channels, on multiple processors, with each channel sending a UDP packet every 20 mSec +/- a couple of mSec. The network stac

We wanted to handle 10's K of VoIP channels, on multiple processors, with each channel sending a UDP packet every 20 mSec +/- a couple of mSec. The network stack was just the standard FreeBSD "box" and had no provision for that kind of clocking or time-to-process guarentees. Our application could call send() on a fixed schedule, but couldn't control when the packet would actually pop out. The process time would vary because of things such as global locks for buffers, varying code paths (do we ARP?), and varying amounts of competition from other processes. The only way to get reasonably consistent times was to way over-provision the system so it was loafing. We were already doing that with Solaris, so not worth it. What we needed was something like Linux's scheduling queue disciplines [0]; it would have allowed us to say "here's a packet, schedule it for 10 mSec from now", and we'd be good as long as the vast majority of packets took less than 10 msec to wend through the stack. But that didn't exist at that point. [0] https://tsn.readthedocs.io/qdiscs.html https://tsn.readthedocs.io/qdiscs.html