From: Zachary Amsden 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 Cc: Andi Kleen Cc: Jeremy Fitzhardinge Cc: Chris Wright Signed-off-by: Andrew Morton --- Documentation/kernel-parameters.txt | 7 +++++-- arch/i386/kernel/io_apic.c | 16 ++++++++++++++-- 2 files changed, 19 insertions(+), 4 deletions(-) diff -puN Documentation/kernel-parameters.txt~paravirt-skip-timer-works Documentation/kernel-parameters.txt --- a/Documentation/kernel-parameters.txt~paravirt-skip-timer-works +++ 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. + noirqtest [IA-32,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 diff -puN arch/i386/kernel/io_apic.c~paravirt-skip-timer-works arch/i386/kernel/io_apic.c --- a/arch/i386/kernel/io_apic.c~paravirt-skip-timer-works +++ a/arch/i386/kernel/io_apic.c @@ -1864,6 +1864,15 @@ static void __init setup_ioapic_ids_from static void __init setup_ioapic_ids_from_mpc(void) { } #endif +int timer_irq_really_works __initdata; +int __init irqtest_disable(char *str) +{ + timer_irq_really_works = 1; + return 1; +} + +__setup("noirqtest", irqtest_disable); + /* * 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: @@ -1872,10 +1881,13 @@ 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 (timer_irq_really_works) + return 1; + local_irq_enable(); /* Let ten ticks pass... */ mdelay((10 * 1000) / HZ); @@ -2146,7 +2158,7 @@ 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; _