linux-kernel - Re: [RFC PATCH] hrtimer: removing all ur callback modes

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Date:	Thu, 4 Dec 2008 11:33:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	oliver@...tkopp.net
Subject: Re: [RFC PATCH] hrtimer: removing all ur callback modes


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, 2008-11-25 at 12:43 +0100, Peter Zijlstra wrote:
> > Hi,
> > 
> > This is an attempt at removing some of the hrtimer complexity by
> > reducing the number of callback modes to 1.
> > 
> > This means that all hrtimer callback functions will be ran from HARD-irq
> > context.
> > 
> > I went through all the 30 odd hrtimer callback functions in the kernel
> > and saw only one that I'm not quite sure of, which is the one in
> > net/can/bcm.c - hence I'm CC-ing the folks responsible for that code.
> > 
> > Furthermore, the hrtimer core now calls callbacks directly with IRQs
> > disabled in case you try to enqueue an expired timer. If this timer is a
> > periodic timer (which should use hrtimer_forward() to advance its time)
> > then it might be possible to end up in an inf. recursive loop due to the
> > fact that hrtimer_forward() doesn't round up to the next timer
> > granularity, and therefore keeps on calling the callback - obviously
> > this needs a fix.
> > 
> > Aside from that, this seems to compile and actually boot on my dual core
> > test box - although I'm sure there are some bugs in, me not hitting any
> > makes me certain :-)
> > 
> > Not-Quite-Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> 
> Ingo, this addition fixes the hotplug issue on my machine

thanks, applied - i also reactivated the tip/timers/hrtimer topic branch 
- lets see how it goes now.

	Ingo
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