This patch implements a sysctl which allows setting a factor, N, for
how many work queue elements can be generated before requiring a
completion event. When a completion event happens the code simulates N
completion events instead of only one. When draining a transmit queue,
N-1 NOPs are transmitted at most, to force generation of the final
completion event. Further a timer is running every HZ ticks to flush
any remaining data off the transmit queue when the tx_completion_fact
> 1.
The goal of this feature is to reduce the PCI bandwidth needed when
transmitting data.
Sponsored by: Mellanox Technologies
Tested by: Netflix
MFC after: 1 week
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