diff options
Diffstat (limited to 'Documentation/nmi_watchdog.txt')
| -rw-r--r-- | Documentation/nmi_watchdog.txt | 16 |
1 files changed, 7 insertions, 9 deletions
diff --git a/Documentation/nmi_watchdog.txt b/Documentation/nmi_watchdog.txt index 757c729ee42e..90aa4531cb67 100644 --- a/Documentation/nmi_watchdog.txt +++ b/Documentation/nmi_watchdog.txt | |||
| @@ -10,7 +10,7 @@ us to generate 'watchdog NMI interrupts'. (NMI: Non Maskable Interrupt | |||
| 10 | which get executed even if the system is otherwise locked up hard). | 10 | which get executed even if the system is otherwise locked up hard). |
| 11 | This can be used to debug hard kernel lockups. By executing periodic | 11 | This can be used to debug hard kernel lockups. By executing periodic |
| 12 | NMI interrupts, the kernel can monitor whether any CPU has locked up, | 12 | NMI interrupts, the kernel can monitor whether any CPU has locked up, |
| 13 | and print out debugging messages if so. | 13 | and print out debugging messages if so. |
| 14 | 14 | ||
| 15 | In order to use the NMI watchdog, you need to have APIC support in your | 15 | In order to use the NMI watchdog, you need to have APIC support in your |
| 16 | kernel. For SMP kernels, APIC support gets compiled in automatically. For | 16 | kernel. For SMP kernels, APIC support gets compiled in automatically. For |
| @@ -22,8 +22,7 @@ CONFIG_X86_UP_IOAPIC is for uniprocessor with an IO-APIC. [Note: certain | |||
| 22 | kernel debugging options, such as Kernel Stack Meter or Kernel Tracer, | 22 | kernel debugging options, such as Kernel Stack Meter or Kernel Tracer, |
| 23 | may implicitly disable the NMI watchdog.] | 23 | may implicitly disable the NMI watchdog.] |
| 24 | 24 | ||
| 25 | For x86-64, the needed APIC is always compiled in, and the NMI watchdog is | 25 | For x86-64, the needed APIC is always compiled in. |
| 26 | always enabled with I/O-APIC mode (nmi_watchdog=1). | ||
| 27 | 26 | ||
| 28 | Using local APIC (nmi_watchdog=2) needs the first performance register, so | 27 | Using local APIC (nmi_watchdog=2) needs the first performance register, so |
| 29 | you can't use it for other purposes (such as high precision performance | 28 | you can't use it for other purposes (such as high precision performance |
| @@ -63,16 +62,15 @@ when the system is idle), but if your system locks up on anything but the | |||
| 63 | "hlt", then you are out of luck -- the event will not happen at all and the | 62 | "hlt", then you are out of luck -- the event will not happen at all and the |
| 64 | watchdog won't trigger. This is a shortcoming of the local APIC watchdog | 63 | watchdog won't trigger. This is a shortcoming of the local APIC watchdog |
| 65 | -- unfortunately there is no "clock ticks" event that would work all the | 64 | -- unfortunately there is no "clock ticks" event that would work all the |
| 66 | time. The I/O APIC watchdog is driven externally and has no such shortcoming. | 65 | time. The I/O APIC watchdog is driven externally and has no such shortcoming. |
| 67 | But its NMI frequency is much higher, resulting in a more significant hit | 66 | But its NMI frequency is much higher, resulting in a more significant hit |
| 68 | to the overall system performance. | 67 | to the overall system performance. |
| 69 | 68 | ||
| 70 | NOTE: starting with 2.4.2-ac18 the NMI-oopser is disabled by default, | 69 | On x86 nmi_watchdog is disabled by default so you have to enable it with |
| 71 | you have to enable it with a boot time parameter. Prior to 2.4.2-ac18 | 70 | a boot time parameter. |
| 72 | the NMI-oopser is enabled unconditionally on x86 SMP boxes. | ||
| 73 | 71 | ||
| 74 | On x86-64 the NMI oopser is on by default. On 64bit Intel CPUs | 72 | NOTE: In kernels prior to 2.4.2-ac18 the NMI-oopser is enabled unconditionally |
| 75 | it uses IO-APIC by default and on AMD it uses local APIC. | 73 | on x86 SMP boxes. |
| 76 | 74 | ||
| 77 | [ feel free to send bug reports, suggestions and patches to | 75 | [ feel free to send bug reports, suggestions and patches to |
| 78 | Ingo Molnar <mingo@redhat.com> or the Linux SMP mailing | 76 | Ingo Molnar <mingo@redhat.com> or the Linux SMP mailing |