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

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Date:	Mon, 08 Dec 2008 17:15:55 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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

On Mon, 2008-12-08 at 17:13 +0100, Peter Zijlstra 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...

Must be monday... can't be -1 if you did the migration.. please double
check, I'm dangerous today :/

> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/hrtimer.c |    8 +-------
 1 files changed, 1 insertions(+), 7 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index b09c7a2..b741f85 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1571,7 +1571,7 @@ static void tickle_timers(void *arg)
 static int __cpuinit hrtimer_cpu_notify(struct notifier_block *self,
 					unsigned long action, void *hcpu)
 {
-	int dcpu = -1, scpu = (long)hcpu;
+	int dcpu, scpu = (long)hcpu;
 
 	switch (action) {
 
@@ -1585,12 +1585,6 @@ static int __cpuinit hrtimer_cpu_notify(struct notifier_block *self,
 	case CPU_DEAD_FROZEN:
 		clockevents_notify(CLOCK_EVT_NOTIFY_CPU_DEAD, &scpu);
 		dcpu = migrate_hrtimers(scpu);
-		break;
-
-	case CPU_POST_DEAD:
-		if (dcpu == -1)
-			break;
-
 		smp_call_function_single(dcpu, tickle_timers, NULL, 0);
 		break;
 #endif

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