Commit 8542b200 authored by Zachary Amsden's avatar Zachary Amsden Committed by Andi Kleen
Browse files

[PATCH] paravirt: Add option to allow skipping the timer check 



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: default avatarZachary Amsden <zach@vmware.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
[chrisw: use no_timer_check to bring inline with x86_64 as per Andi's request]
Signed-off-by: default avatarChris Wright <chrisw@sous-sol.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
parent 8ecb8950

Documentation/kernel-parameters.txt

+5 −2
Original line number Diff line number Diff line
@@ -599,8 +599,6 @@ and is between 256 and 4096 characters. It is defined in the file 


	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
@@ -1052,9 +1050,14 @@ and is between 256 and 4096 characters. It is defined in the file 
			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

arch/i386/kernel/io_apic.c

+14 −2
Original line number Diff line number Diff line
@@ -1932,6 +1932,15 @@ static void __init setup_ioapic_ids_from_mpc(void) 
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:
@@ -1940,10 +1949,13 @@ static void __init setup_ioapic_ids_from_mpc(void) { } 
 *	- 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);
@@ -2214,7 +2226,7 @@ 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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