+ * So, possible solutions:
+ *
+ * (1) tick in realtime. Not very good, because this ticker is used for
+ * profiling, and this will give us unreliable time profiling
+ * results. Furthermore, this requires picking a single OS thread
+ * to be the timekeeper, which is a bad idea because the thread in
+ * question might just be making a temporary call into Haskell land.
+ *
+ * (2) save/restore the virtual timer around excursions into STG land.
+ * Sounds great, but I tried it and the resolution of the virtual timer
+ * isn't good enough (on Linux) - most of our excursions fall
+ * within the timer's resolution and we never make any progress.
+ *
+ * (3) have a virtual timer in every OS thread. Might be reasonable,
+ * because most of the time there is only ever one of these
+ * threads running, so it approximates a single virtual timer.
+ * But still quite bogus (and I got crashes when I tried this).
+ *
+ * For now, we're using (1), but this needs a better solution. --SDM