lttv display questions

I'm using linux 2.6.30-rc5, lttv 0.12.14-15052009, and lttctl 0.64-14012009

What is the meaning of the dots about the graph lines for thread in the "Control Flow Viewer"?

When I start up, I see a number of errors like:

** (lttv.real:24284): WARNING **: No channel for marker named block._blk_request_complete
found

and

** (lttv.real:24284): WARNING **: 5521 events lost so far in tracefile /tmp/t2/vm_state_0
at block 1


Is there anything I can do to cut down on the lost events?

Thanks,

	Andy