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

[Davide Libenzi]

On 21-Sep-2001 Dan Kegel wrote:
> Davide wrote:
>> If you need to request the current status of 
>> a socket you've to f_ops->poll the fd.
>> The cost of the extra read, done only for fds that are not "ready", is nothing
>> compared to the cost of a linear scan with HUGE numbers of fds.
> 
> Hey, wait a sec, Davide... the whole point of the Solaris /dev/poll
> is that you *don't* need to f_ops->poll the fd, I think.
> And in fact, Solaris /dev/poll is insanely fast, way faster than O(N).

If the fd support hints, yes.

> Consider this: what if we added to your patch logic to clear
> the current read readiness bit for a fd whenever a read() on
> that fd returned EWOULDBLOCK?  Then we're real close to having
> the current readiness state for each fd, as the /dev/poll afficianados 
> want.  Now, there's a lot more work that'd be needed, but maybe you
> get the idea of where some of us are coming from.

Then you'll fall down to /dev/poll and /dev/epoll designed for "state change"
driven servers ( like rtsigs ).
Instead of requesting /dev/epoll changes to make it something that is not born for,
i think that the /dev/poll patch can be improved in a significant way.
The numbers i've got from my test left me quite a bit deluded.

- Davide