tested on mac only.
output like this:
	tubenose=% sudo go/src/cmd/prof/6prof -p 71839 -c  -d 10
	63.93%	mach_semaphore_signal
	 4.64%	sys·chansend1
	 3.93%	chanrecv
	 2.86%	semrelease
	 1.43%	cas
	 1.43%	sendchan
	 1.07%	xadd
	 0.71%	main·f
	 0.71%	scheduler
	 0.71%	sys·gosched
	 0.71%	dequeue
	 ...

R=rsc
DELTA=361  (361 added, 0 deleted, 0 changed)
OCL=15731
CL=15736