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

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Message-ID: <cfd18e0f0902091501g5059a12s3dc734d9a936890a@mail.gmail.com>
Date:	Tue, 10 Feb 2009 12:01:50 +1300
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Davide Libenzi <davidel@...ilserver.org>
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, Feb 10, 2009 at 9:10 AM, Davide Libenzi <davidel@...ilserver.org> wrote:
> 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.

Okay, thanks for the info.  I've added some text to the
timerfd_create(2) page to explicitly note that the range of clocks
supported by timerfd_create() is smaller than POSIX timers.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
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