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SubjectRe: > 15,000 Simultaneous Connections
On 6 Sep 1999, Andreas Schwab wrote:

> Mike Jagdis <mike@roan.co.uk> writes:
>
> |> The main cost of select and poll, on the kernel side, is scanning
> |> the fds to see what is ready. The way select and poll are usually
> |> used we want a means to express an interest in an fd and then
> |> receive a stream of "events" as fds change state.
>
> That's what SIGIO is for.

Partly. But you want to ask for a real time signal to be used
so that you get the fd as well. Then there's a limit on the
number of signals that can be queued at once and, I think, if
you hit the limit signals get dropped (or turned into non-queuing
SIGINFO) which can be a problem. Plus sharing the signal queue
between tasks/{processes,threads} isn't possible. And if you
are delivering to a process group each process gets its own
siginfo allocated and queued. Then there's all the signal
code adding to the overhead on each event. Yup, signals are
an option, but they have their own set of gotchas and scalability
issues which are probably even less well understood than
select and poll :-).

Mike

--
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On my desk I have a work station...
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