In this case, 64k TSO becomes a liability and it will make sense to limit it.
TSO "sweet spot" will be captured anyways - at least on fast networks, going
from 1.5k to 9k typically doubles throughput, while going from 9k to 64k
adds no more than another 10% (plus a little bit of free %cpu, but not that
much).
On the surface, that just sounds like something adhering to the laws of
diminishing returns. As you increase the TSO size, you are shrinking the
per-send costs, but the per-byte costs (if there is a copy from user to kernel)
and the ack costs remain the same.
If that 1500 to 9K to 64K is an MTU (and thus real MSS) change than the per-send
and ack costs are what are diminishing but the per-byte costs remain the same.
Asymptotes and all that...
rick jones
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