I was playing whistle along with a fiddle tune today, and found fast octave jumps to be the trickiest part (in this case, low B to high B, back and forth a few times). on viol-, er, fiddle, this is plenty easy, but fast over blowing and delicate blowing on whistle seems to be much tougher.
any tips i need to be aware of?
For me, I tongue using a “d” sound instead of the “t” sound. Or maybe trying to push a little with your stomach (diaphram?) for that extra push of air needed to jump octaves.
I find a cut sometimes helps. Or helps disguise the transition at least. I may not be appropriate in your tune, and it may not be good/acceptable technique though. I am thinking purely about the mechanics of it…
A similar effect can be got by going from the B → a → b. It is still a disguise, I guess, but for me a pleasant disguise or cheat is better than a unpleasant attempt at the right thing.
i find going low to high easy enough, but dropping low again, or bouncing back and forth is what’s tricky for me.
The flute has the same challenge; the great flute (and whistle) player Kevin Crawford talks about having to “stop in mid-flight” to make the transition from a note in the second octave to the same note in the first. Basically you place a stop at the end of the high note, either with your tongue or a glottal stop, and then take a fresh attack on the lower note. You just need to cut off the airflow at the end of the high note; it makes it much easier to obtain a strong low note than if you try to slur the notes by reducing the airflow without a stop.
good input guys, thanks! 
Cover 1/3rd of the bore end hole with tape to improve backpressure. This will allow faster octave jumps. Also try the "O"ring tweak to create backpressure at the top of the labium ramp (Larger ring is better).
I’m with BradHurley on this topic. The glottal is the best way to divide octaves on certain notes - I’m not sure how fast you’re taking this, but the point is to make it clean and to voice each note in order to attain the octave effect.
A glottal can be described as a back throated ‘UGH’ - which give you time to adjust the pressure needed for the note. (It takes some practice, just like a low D roll takes practice)