Re: [PATCH] /dev/epoll update ...

[Davide Libenzi]

On 24-Sep-2001 Jamie Lokier wrote:
> Davide Libenzi wrote:
>> > You could even keep the memory for the queued signal / event inside
> the file structure.
>> 
>> By keeping the event structure inside the file* require you to collect
>> these events ( read memory moves ) at peek time.
>> With /dev/epoll the event is directly dropped inside the mmaped area.
> 
> Well, memory move consists of 2 words: (a) file descriptor; (b) poll
> state/edge flags.

2-words * number-of-ready-fds == pretty-high-cache-drain

> That will be completely swamped by the system calls and so on needed to
> processes each of the file descriptors.  I.e. no scalability problem here.

The other issue is that by keeping infos in file* you'll have to scan each fd
to report the ready ones, that will make the method to fall back in O(n).
Anyway there's a pretty good patch ( http://www.luban.org/GPL/gpl.html ),
that has been tested here :

http://www.xmailserver.org/linux-patches/nio-improve.html

that implement the signal-per-fd mechanism and it achieves a very good scalability too.

- Davide