Reducing select() usage under load

Erik Rozendaal erik at
Fri May 12 19:41:11 UTC 2006

Aaron Hopkins wrote:
> It is hard and expensive if you want to ensure perfect fairness and
> interleave responses from every socket.  But I think there a compromise
> available between perfect fairness and only answering requests from one
> socket when it is flooded.
> Changing that while(1) I added to something that would only loop up to a
> fixed number of times (e.g. 100) would be trivial.  You'd still amortize 
> the
> cost of the select() over many UDP packets, without being able to starve
> other sockets for more than a few milliseconds.  You'd concentrate on work
> from one socket, then switch to the next one and do everything pending 
> up to
> the same limit.  And the performance gains would be approximately the same.

Yes, that could certainly work. And like you measured, saving on 
select() makes a huge difference for NSD since it spends a lot of its 
time in system calls :)


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