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

[Dan Kegel]

Jamie Lokier wrote:
> > 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.
> 
> It has the bonus of requiring no userspace changes too.  Lovely!

Well, not quite *no* userspace changes, but not many.  You have to
use si_band rather than si_code (and with Luban's version, you also
need to set a new flag).

It has some locking problems that only show up under very heavy use,
so caveat emptor.  I put together a stress test 
(http://www.kegel.com/dkftpbench/ with the -sf option);
run that against betaftpd, and around 4500 ftp sessions, you might
see it crash because a signal comes in while the file table is expanding...

(By the way, I finally updated http://www.kegel.com/c10k.html to
distinguish properly between edge-triggered readiness notification
methods and level-triggered ones.  Hope that helps dispel some 
confusion in the future.)
- Dan