linux-kernel - Re: [patch-mm 01/25] NOHZ: Fix nox x86 dyntick idle handling

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Date:	Sat, 16 Jun 2007 16:54:43 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Bernhard Rosenkraenzer <bero@...linux.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Chris Wright <chrisw@...s-sol.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Adam Belay <abelay@...ell.com>, Len Brown <lenb@...nel.org>,
	Dave Miller <davem@...emloft.net>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [patch-mm 01/25] NOHZ: Fix nox x86 dyntick idle handling

On Sat, 2007-06-16 at 16:36 +0200, Bernhard Rosenkraenzer wrote:
> On Saturday 16 June 2007, Thomas Gleixner wrote:
> 
> > +#if defined(CONFIG_NO_HZ) && !defined(CONFIG_NONIRQ_WAKEUP)
> > +	/* Make sure that timer wheel updates are propagated */
> > +	if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
> > +		tick_nohz_stop_sched_tick();a
> > +#endif
> >  	preempt_enable_no_resched();
> >  }
> 
> The bit above breaks the build for a CONFIG_NO_HZ build without 
> CONFIG_NONIRQ_WAKEUP -- please remove the extra "a" after 
> tick_nohz_stop_sched_tick(); before applying this.

Oops. Must have happened when I edited the mailbox. Replacement patch
below:

	tglx

--------------------->

Subject: NOHZ: Fix nox x86 dyntick idle handling

The cpuidle patches moved the tick nohz handling from irq_exit into
the inner idle loop. The change is correct as it covers non interrupt
based wakeups (e.g DMA) on x86 as well, but the move breaks ARM, SH
and SPARC64. 

Keep the original implementation and deselet the irq exit code for
those architectures which have no irq idle wakeups.

This way the non affected architectures are not burdened with the
extra changes in the idle implementation.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Adam Belay <abelay@...ell.com>
Cc: Len Brown <lenb@...nel.org>
Cc: Dave Miller <davem@...emloft.net>
Cc: Paul Mundt <lethal@...ux-sh.org>
Cc: Russell King <rmk+kernel@....linux.org.uk>

---
 arch/i386/Kconfig |    4 ++++
 kernel/softirq.c  |    5 +++++
 2 files changed, 9 insertions(+)

Index: linux-2.6.22-rc4-mm/arch/i386/Kconfig
===================================================================
--- linux-2.6.22-rc4-mm.orig/arch/i386/Kconfig	2007-06-16 17:04:14.000000000 +0200
+++ linux-2.6.22-rc4-mm/arch/i386/Kconfig	2007-06-16 17:04:18.000000000 +0200
@@ -31,6 +31,10 @@ config GENERIC_CLOCKEVENTS_BROADCAST
 	default y
 	depends on X86_LOCAL_APIC
 
+config NONIRQ_WAKEUP
+	bool
+	default y
+
 config LOCKDEP_SUPPORT
 	bool
 	default y
Index: linux-2.6.22-rc4-mm/kernel/softirq.c
===================================================================
--- linux-2.6.22-rc4-mm.orig/kernel/softirq.c	2007-06-16 17:04:14.000000000 +0200
+++ linux-2.6.22-rc4-mm/kernel/softirq.c	2007-06-16 17:04:39.000000000 +0200
@@ -304,6 +304,11 @@ void irq_exit(void)
 	if (!in_interrupt() && local_softirq_pending())
 		invoke_softirq();
 
+#if defined(CONFIG_NO_HZ) && !defined(CONFIG_NONIRQ_WAKEUP)
+	/* Make sure that timer wheel updates are propagated */
+	if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
+		tick_nohz_stop_sched_tick();
+#endif
 	preempt_enable_no_resched();
 }
 


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