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SubjectRe: [PATCH 1/5] Skip timer works.patch
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
_
-
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