linux-kernel - Re: [patch 2/2] timerfd extend clockid support

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Message-ID: <alpine.DEB.1.10.0902091148520.8503@alien.or.mcafeemobile.com>
Date:	Mon, 9 Feb 2009 12:10:23 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	mtk.manpages@...il.com
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 2/2] timerfd extend clockid support

On Tue, 10 Feb 2009, Michael Kerrisk wrote:

> > and I did not have even the time to peek
> > into the core timer code to see if the usage of other timer types in
> > eventfd would create problems. That's why I asked Thomas if they'd behave
> > differently from an hrtimer caller POV.
> > I'll try to take a look by myself today or tomorrow.
> 
> Okay -- hopefully my test program may be useful (even if it is not
> itself fully tested yet, it's patterned after a similar test program I
> wrote fot the POSIX timers API, so it should mostly work).

Answer was pretty easy once you look at the code :)
Timerfd uses core hrtimer functions, and clockids different from the ones 
timerfd already handles, fall into the CPU-timers domain. Domain that is 
not handled by hrtimer.
Changes to timerfd to support CPU-based timers are really deep (more than 
changes, is a total rewrite). not only to timerfd, but also to CPU-based 
timers to deliver notification by means different than signals.
Given the amount of code change, and given that a posix-timers->signalfd 
bridge could solve the problem, I'm not going even close to suggest such a 
change.

- Davide

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