Proposal to compile in delayed ACK support by default

[Terry Burton]

Hi,

ISC recommends the use of delayed-ack [1] yet this feature is still
described as experimental and is omitted from the build by default.

Myself and others [2] have had success with this feature and I would
like to see --enable-delayed-ack become default (as least in
distributions which typically follow the upstream behaviour). However
this poses an upgrade risk because the runtime default configuration
would currently enable this code path.

How would the following proposal be received?

* Change the default delayed-ack count parameter from 28 to 0.
* Use delayed-ack == 0 as a guard to short-circuit across the
delayed_ack_enqueue code.
* Compile with delayed-ack support by default. (In fact, probably just
make this unconditional as the routines are currently compiled in even
when they are unreachable.)

An untested patch illustrating this is attached...


[1] https://deepthought.isc.org/article/AA-00373/0/Synchronous-Disk-Writes-and-DHCP-Performance-Limitations.html
[2] https://lists.isc.org/pipermail/dhcp-users/2014-November/018387.html


All the best,

Terry
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