Here's something I did last year and then put on ice, partly
through lack of time and partly because I thought I'd pick
it up for 2.5.
All this talk of event queues misses one thing: we already
have an event queue mechanism. They're called wait queues.
The only problem is that the only on-event action possible
is to wake the process (assuming it was asleep in the first
place). This patch firstly extends the wait queue mechanism
to allow an arbitrary action to be performed. Then I rewrote
the select/poll implementation to use event queueing to avoid
rescanning descriptors that had not changed - and restructured
the loops to be rather more efficient. This approach doesn't
need any changes to driver poll routines, it doesn't need
backwards mapping struct files. It should be fairly easy to
implement a /dev/poll mechanism using this, although I haven't
yet.
Yes, the change to wait queues has a slight cost, but it isn't
great and the main part of it only happens if you actually sleep.
Performance graphs and the lmbench derived test programs I
used are at http://www.purplet.demon.co.uk/linux/select/ (bounce
in and out of the index page 'cos the next and prev buttons
aren't wired up :-) )
Oh, and I updated this patch for 2.4.0-test9.
Comments and opinions are, as always, welcome :-).
Mike
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