From: Ben Greear <redacted>
Date: Thu, 26 Aug 2010 22:58:41 -0700

And if it does that, then something must know how to restart the
transmit logic.

When SKBs get freed up, space opens up in the socket send buffer,
waking up the process or signalling it from poll() so it can write
more.

pktgen eliminates this whole layer of queueing and signalling, which
is why it continually succeptible this behavior you dislike.