I/O Limiter Question

What exactly do the I/O tokens correspond to? Is it based strictly on transfer rate, or are all disk requests (e.g. lseek and so on) affected by it?

I've noticed that when I try to seed a BitTorrent session from my Linode 128, that it will initially drain tokens slowly enough that the count stays near 400000, even when I have my maximum upload speed set to 500KB/sec. However, as more people join, the BT client starts sucking up I/O tokens like they're going out of style. I'm guessing that it has to do with file seeks to serve up lots of different file chunks that aren't already buffered to different peers, since I've watched vmstat and not seen any significant swap activity. Eventually, I have to drop the seed down to ridiculously slow (dialup-level) speeds or hit the pause button to replenish tokens.

Any ideas on how I could stop this problem from happening?