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

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Date:	Mon, 8 Dec 2008 17:18:07 +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 Thu, 2008-12-04 at 11:17 +0100, Peter Zijlstra 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
> 
> And because we're all human...
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/hrtimer.c |    5 +----
>  1 files changed, 1 insertions(+), 4 deletions(-)

applied, thanks!

Sidenote: this fix was brought to us by watching new warnings in 
tip/master, where this new one popped up:

 kernel/hrtimer.c: In function ‘hrtimer_cpu_notify’:
 kernel/hrtimer.c:1574: warning: unused variable ‘dcpu’

trying to map dcpu then highlighted the bug.

	Ingo
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