Templin, Fred L wrote:
Have you learned enough about Moore's law that, at 10Gbps era, 72us of delay is often significant?
I frankly haven't thought about it any further.
That's your problem.
You say 1280+ belongs in ITU, and I say 1280- belongs in ATM.
As I already said, 9KB is fine for me. Small cell size (32~48B, not 1280-) of ATM is derived from slow (64Kbps voice) speed and short (0.1s) delay requirement with fair queuing and has no relevance to today's network.
Larger packets means fewer interrupts and fewer packets in flight, which is good Moore's law or no.
That is a basic misunderstanding of those who thought jumbograms were good. They (or you) thought supercomputers are vector computers, very slow to react against interrupts, and have no IO processors to take care of packet handling. The reality with Moore's law, however, is that NIC cards can take care of even TCP, which makes jumbograms totally unnecessary. Moreover, the huge number of scalar processors in modern supercomputers means communication granularity is (depending on computation algorithm) often tiny, which means networks in supercomputers must be able to handle small packets efficiently. Larger packets means, in addition to longer HOL blocking, more delay to pack more data in the packets, even though processors often want to receive data with less delay. Thus, as with other features of IPv6, jumbograms are no useful but harmful. Masataka Ohta