Re: {sys_,/dev/}epoll waiting timeout

[Jamie Lokier <jamie@shareable.org>]

Davide Libenzi wrote:
> >From a mathematical point of view this is a ceil(v)+1, so this is wrong.
> It should be :
> 
> t = (t * HZ + 999) / 1000;
> 
> The +999 already gives you the round up.  Different is if we want to be
> sure to sleep at least that amount of jiffies ( the rounded up ), in that
> case since the timer tick might arrive immediately after we go to sleep by
> making us to lose immediately a jiffie, we need another +1. Anyway I'll do
> the round up. Same for the overflow check.

I wonder if it's appropriate to copy sys_poll(), which has the +1, or
sys_select(), which doesn't!

> > And that the prototypes for ep_poll() and sys_epoll_wait() be changed
> > to take a "long timeout" instead of an "int", just like sys_poll().
> 
> I don't see why. The poll(2) timeout is an int.

poll(2) takes an int, but sys_poll() takes a long.
I think everyone is confused :)

The reason I suggested "long timeout" for ep_poll is because the
multiply in the expression:

	jtimeout = (unsigned long)(timeout*HZ+999)/1000;

can overflow if you don't.  If you stick with the int, you'll need to
write:

	jtimeout = (((unsigned long)timeout)*HZ+999)/1000;

-- Jamie