NAPI enables a software polling mode, or software interrupt migitation
if you prefer to call it that. It kicks in at moderate to high packet
rates, allows the net stack to more globally balance net traffic, and
avoids problems associated with high packet load / DoS situations which
would otherwise max out a cpu.
But it's a new feature, so being conservative there is a staged rollout,
with NAPI support in e100 being an option that can be turned off.
Some drivers like tg3 simply always enable NAPI.
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