Cell Relay Archive

[ashfaq@ipoint.vlsi.uiuc.edu (Ashfaq Hossain)]

I have been thinking about the following basic observation:

	"When the user-level packet size is increased beyond
	 some point, CPU utilization decreases."

Why does this happen?  I am thinking of user-level pkt sizes
(much) larger than the underlying MTU size.  

I know the following:

	1.  For a packet transfer, the overheads can be grouped 
		into 2 major categories:  per-byte overhead and 
		per-message overhead.

	2.  per-message overhead remains reasonably constant 
		with increasing pkt size.

	3.	per-byte overhead increases with pkt size (checksum 
		calculation, user-to-kernel copy etc.)


Will anyone please shed some light on the underlying reason?


Thanks.