Re: RFC: A revised timerfd API

[Thomas Gleixner <tglx@linutronix.de>]

On Sat, 2007-09-22 at 18:07 +0200, Michael Kerrisk wrote:
> Hello Bernd,
> 
> Please don't trim the CC list when replying!  I nearly did not see
> your reply, and others will have missed it also.

Yup.

> On 9/22/07, Bernd Eckenfels <ecki@lina.inka.de> wrote:
> > In article <46F514C9.5010208@gmx.net> you wrote:
> > >  1. This design stretches the POSIX timers API in strange
> > >     ways.
> >
> > Maybe it is possible to reimplement the POSIX API in usermode using the
> > kernel's FD implementation?

Yikes.

> It's a clever idea...  Without thinking on it too long, I'm not sure
> whether or not there might be some details which would make this
> difficult.

You'd need be quite masochistic to start such a project. The POSIX timer
API consists mostly of corner cases and I doubt that you get them even
halfway under control in a pure user space implementation.

It would be a rather huge performance penalty as well. You need at least
two user space context switches to get the most simple cases resolved.

> > (and drop the posix support from kernel)
> 
> However we couldn't drop POSIX support from the kernel, because that
> would break the ABI.

True. So there is no point in reinventing the wheel.

	tglx