a proposed callout API

[Poul-Henning Kamp]

In message <20061113133236.A28926 at xorpc.icir.org>, Luigi Rizzo writes:
>On Mon, Nov 13, 2006 at 08:53:41PM +0000, Poul-Henning Kamp wrote:
>> 

>i am a bit curious on why  you want to split the callouts among
>multiple data structures.

A binary heap is optimal for the timeouts that will happen, but
filling it up with timeouts that are unlikely to, and in most
cases won't happen for a very long time will soak up CPU
time used for pointlessly ordering the heap.

Also, many of the "non-happening" timeouts are repeatedly
rescheduled, the TCP keepalives for instance, having a data structure
where this is free of cost is a big advantage.

The other thing is that covering the entire range from hour long
callouts to nanosecond callouts would require a 64 bit value or
a tricky pseudo-FP encoding.  By splitting them in two classes,
I can use two different 31 bit encodings separated by the top bit.

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