linux-kernel - Re: [PATCH 12/13] hrtimer: create a "timer

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Message-ID: <20080908072220.75fc3dfd@infradead.org>
Date:	Mon, 8 Sep 2008 07:22:20 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Pavel Machek <pavel@...e.cz>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	dwmw2@...radead.org, drepper@...hat.com, mingo@...e.hu,
	tglx@...x.de
Subject: Re: [PATCH 12/13] hrtimer: create a "timer_slack" field in the task
 struct

On Mon, 8 Sep 2008 16:15:55 +0200
Pavel Machek <pavel@...e.cz> wrote:

> On Mon 2008-09-08 06:40:02, Arjan van de Ven wrote:
> > On Mon, 8 Sep 2008 15:27:16 +0200
> > Pavel Machek <pavel@...e.cz> wrote:
> > > > 
> > > > ... which nobody uses today.
> > > > It's not just new syscalls, it's a new glibc api as well at that
> > > > point.
> > > 
> > > ...and new applications, yes. I believe applications should
> > > explicitely enable slacking timers.
> > 
> > timers are slacking today, at least for select() and poll(), and
> > are a great deal more so than the defaults in this patchkit.
> 
> Ok, so select()/poll() may default to non-zero slack for legacy apps.

that's whats there
> 
> > The great advantage of the prctl() approach (which is usable) over
> > new system calls and glibc APIs is that it will get used, because
> > the admin can use it just like he uses the "nice" command, on
> > existing software.
> 
> Yes, it is a great advantage, but it feels like a hack. Maybe it is
> better done with LD_PRELOAD or something?

that's not working very well in general, and doesn't work across exec
etc.

> 
> I'd certianly want the applications to specify slack themselves in
> like 10 years.

We've been talking to Ulrich to figure out what the right API for this
is (eg how to extend select/poll for this) and I still plan to work on
this, but both Linus and Ulrich seem to be very ademant that it means
only few apps will use it (and I agree with that, just look at how many
apps use linux specific APIs such as sendfile(), linux AIO etc... )


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