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

Davide Libenzi (
Mon, 24 Sep 2001 15:20:11 -0700 (PDT)

On 24-Sep-2001 Jamie Lokier wrote:
> Davide Libenzi wrote:
>> > 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
> Perhaps there is a cache issue, but note it is the number of _new_ ready
> fds (since the last sample), not the number currently ready.
>> > 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).
> No, that would be silly. You would queue signals exactly as they are
> queued now (but collapsing multiple signals per fd into one).
>> Anyway there's a pretty good patch ( ),
>> that has been tested here :
>> that implement the signal-per-fd mechanism and it achieves a very good
>> scalability too.
> It has the bonus of requiring no userspace changes too. Lovely!

Sure you can avoid the scan, if you pick up one event at a time.
To be compared to /dev/epoll you need the signal-per-fd patch plus a method to
collect the whole event-set in a single system call ( see perfs ).

- Davide

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