linux-kernel - Re: [PATCH 1/5] Skip timer works.patch

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Date:	Wed, 15 Nov 2006 00:03:23 -0800
From:	Chris Wright <chrisw@...s-sol.org>
To:	Andi Kleen <ak@....de>
Cc:	Zachary Amsden <zach@...are.com>, Andi Kleen <ak@...e.de>,
	virtualization@...ts.osdl.org, Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] Skip timer works.patch

* Andi Kleen (ak@....de) wrote:
> On Mon, Oct 30, 2006 at 12:54:55PM -0800, Zachary Amsden wrote:
> > Andi Kleen wrote:
> > >no_timer_check. But it's only there on x86-64 in mainline - although there
> > >were some patches to add it to i386 too.
> > >  
> > 
> > I can rename to match the x86-64 name.
> 
> I will do that in my tree.

Looks like this one might have been lost.  Here's the renamed version
(it's against 2.6.19-rc5-mm2, which should have your tree in it).

thanks,
-chris
--

From: Zachary Amsden <zach@...are.com>

Add a way to disable the timer IRQ routing check via a boot option.  The
VMI timer code uses this to avoid triggering the pester Mingo code, which
probes for some very unusual and broken motherboard routings.  It fires
100% of the time when using a paravirtual delay mechanism instead of
using a realtime delay, since there is no elapsed real time, and the 4 timer
IRQs have not yet been delivered.

In addition, it is entirely possible, though improbable, that this bug
could surface on real hardware which picks a particularly bad time to enter
SMM mode, causing a long latency during one of the timer IRQs.

While here, make check_timer be __init.

Signed-off-by: Zachary Amsden <zach@...are.com>
[chrisw: use no_timer_check to bring inline with x86_64 as per Andi's request]
Signed-off-by: Chris Wright <chrisw@...s-sol.org>

===================================================================
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -610,8 +610,6 @@ and is between 256 and 4096 characters. 
 
 	hugepages=	[HW,IA-32,IA-64] Maximal number of HugeTLB pages.
 
-	noirqbalance	[IA-32,SMP,KNL] Disable kernel irq balancing
-
 	i8042.direct	[HW] Put keyboard port into non-translated mode
 	i8042.dumbkbd	[HW] Pretend that controller can only read data from
 			     keyboard and cannot control its state
@@ -1081,8 +1079,13 @@ and is between 256 and 4096 characters. 
 			in certain environments such as networked servers or
 			real-time systems.
 
+	noirqbalance	[IA-32,SMP,KNL] Disable kernel irq balancing
+
 	noirqdebug	[IA-32] Disables the code which attempts to detect and
 			disable unhandled interrupt sources.
+
+	no_timer_check	[IA-32,X86_64,APIC] Disables the code which tests for
+			broken timer IRQ sources.
 
 	noisapnp	[ISAPNP] Disables ISA PnP code.
 
===================================================================
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -1931,6 +1931,15 @@ static void __init setup_ioapic_ids_from
 static void __init setup_ioapic_ids_from_mpc(void) { }
 #endif
 
+static int no_timer_check __initdata;
+
+static int __init notimercheck(char *s)
+{
+	no_timer_check = 1;
+	return 1;
+}
+__setup("no_timer_check", notimercheck);
+
 /*
  * There is a nasty bug in some older SMP boards, their mptable lies
  * about the timer IRQ. We do the following to work around the situation:
@@ -1939,9 +1948,12 @@ static void __init setup_ioapic_ids_from
  *	- if this function detects that timer IRQs are defunct, then we fall
  *	  back to ISA timer IRQs
  */
-static int __init timer_irq_works(void)
+int __init timer_irq_works(void)
 {
 	unsigned long t1 = jiffies;
+
+	if (no_timer_check)
+		return 1;
 
 	local_irq_enable();
 	/* Let ten ticks pass... */
@@ -2219,7 +2231,7 @@ int timer_uses_ioapic_pin_0;
  * is so screwy.  Thanks to Brian Perkins for testing/hacking this beast
  * fanatically on his truly buggy board.
  */
-static inline void check_timer(void)
+static inline void __init check_timer(void)
 {
 	int apic1, pin1, apic2, pin2;
 	int vector;
-
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