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

[Andrew Morton <akpm@osdl.org>]

On Thu, 19 Oct 2006 17:09:22 -0700
Zachary Amsden <zach@vmware.com> wrote:

> 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.
> 

Andi seems to have merged this patch but from somewhere I picked up a
different version, below.

I think the version I have is better.  Because the patch Andi has merged is
cast in terms of "irq testing", which is broad.  But that's not what the
patch does - the patch handles only timers.

IOW, this:

> +
> +	noirqtest	[IA-32,APIC] Disables the code which tests for broken
> +			timer IRQ sources.

is misleadingly named.  This:

+       no_timer_check  [IA-32,X86_64,APIC] Disables the code which tests for
+                       broken timer IRQ sources.
+

is better, no?

But right now, I'll settle for anything which usually compiles.



From: Zachary Amsden <zach@vmware.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@vmware.com>
[chrisw: use no_timer_check to bring inline with x86_64 as per Andi's request]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 Documentation/kernel-parameters.txt |    7 +++++--
 arch/i386/kernel/io_apic.c          |   16 ++++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff -puN arch/i386/kernel/io_apic.c~i386-add-a-way-to-disable-the-timer-irq-routing-check-via-a-boot-option arch/i386/kernel/io_apic.c
--- a/arch/i386/kernel/io_apic.c~i386-add-a-way-to-disable-the-timer-irq-routing-check-via-a-boot-option
+++ a/arch/i386/kernel/io_apic.c
@@ -1930,6 +1930,15 @@ 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:
@@ -1938,10 +1947,13 @@ 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... */
 	mdelay((10 * 1000) / HZ);
@@ -2212,7 +2224,7 @@ 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;
diff -puN Documentation/kernel-parameters.txt~i386-add-a-way-to-disable-the-timer-irq-routing-check-via-a-boot-option Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~i386-add-a-way-to-disable-the-timer-irq-routing-check-via-a-boot-option
+++ a/Documentation/kernel-parameters.txt
@@ -599,8 +599,6 @@ 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
@@ -1056,9 +1054,14 @@ 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.
 
 	noinitrd	[RAM] Tells the kernel not to load any configured
_