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-rw-r--r--Documentation/sysctl/kernel.txt83
1 files changed, 74 insertions, 9 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 83ab25660fc9..c831001c45f1 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -77,12 +77,14 @@ show up in /proc/sys/kernel:
- shmmax [ sysv ipc ]
- shmmni
- softlockup_all_cpu_backtrace
+- soft_watchdog
- stop-a [ SPARC only ]
- sysrq ==> Documentation/sysrq.txt
- sysctl_writes_strict
- tainted
- threads-max
- unknown_nmi_panic
+- watchdog
- watchdog_thresh
- version
@@ -417,16 +419,23 @@ successful IPC object allocation.
nmi_watchdog:
-Enables/Disables the NMI watchdog on x86 systems. When the value is
-non-zero the NMI watchdog is enabled and will continuously test all
-online cpus to determine whether or not they are still functioning
-properly. Currently, passing "nmi_watchdog=" parameter at boot time is
-required for this function to work.
+This parameter can be used to control the NMI watchdog
+(i.e. the hard lockup detector) on x86 systems.
-If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel
-parameter), the NMI watchdog shares registers with oprofile. By
-disabling the NMI watchdog, oprofile may have more registers to
-utilize.
+ 0 - disable the hard lockup detector
+ 1 - enable the hard lockup detector
+
+The hard lockup detector monitors each CPU for its ability to respond to
+timer interrupts. The mechanism utilizes CPU performance counter registers
+that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
+while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
+
+The NMI watchdog is disabled by default if the kernel is running as a guest
+in a KVM virtual machine. This default can be overridden by adding
+
+ nmi_watchdog=1
+
+to the guest kernel command line (see Documentation/kernel-parameters.txt).
==============================================================
@@ -816,6 +825,22 @@ NMI.
==============================================================
+soft_watchdog
+
+This parameter can be used to control the soft lockup detector.
+
+ 0 - disable the soft lockup detector
+ 1 - enable the soft lockup detector
+
+The soft lockup detector monitors CPUs for threads that are hogging the CPUs
+without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads
+from running. The mechanism depends on the CPUs ability to respond to timer
+interrupts which are needed for the 'watchdog/N' threads to be woken up by
+the watchdog timer function, otherwise the NMI watchdog - if enabled - can
+detect a hard lockup condition.
+
+==============================================================
+
tainted:
Non-zero if the kernel has been tainted. Numeric values, which
@@ -847,6 +872,27 @@ can be ORed together:
==============================================================
+threads-max
+
+This value controls the maximum number of threads that can be created
+using fork().
+
+During initialization the kernel sets this value such that even if the
+maximum number of threads is created, the thread structures occupy only
+a part (1/8th) of the available RAM pages.
+
+The minimum value that can be written to threads-max is 20.
+The maximum value that can be written to threads-max is given by the
+constant FUTEX_TID_MASK (0x3fffffff).
+If a value outside of this range is written to threads-max an error
+EINVAL occurs.
+
+The value written is checked against the available RAM pages. If the
+thread structures would occupy too much (more than 1/8th) of the
+available RAM pages threads-max is reduced accordingly.
+
+==============================================================
+
unknown_nmi_panic:
The value in this file affects behavior of handling NMI. When the
@@ -858,6 +904,25 @@ example. If a system hangs up, try pressing the NMI switch.
==============================================================
+watchdog:
+
+This parameter can be used to disable or enable the soft lockup detector
+_and_ the NMI watchdog (i.e. the hard lockup detector) at the same time.
+
+ 0 - disable both lockup detectors
+ 1 - enable both lockup detectors
+
+The soft lockup detector and the NMI watchdog can also be disabled or
+enabled individually, using the soft_watchdog and nmi_watchdog parameters.
+If the watchdog parameter is read, for example by executing
+
+ cat /proc/sys/kernel/watchdog
+
+the output of this command (0 or 1) shows the logical OR of soft_watchdog
+and nmi_watchdog.
+
+==============================================================
+
watchdog_thresh:
This value can be used to control the frequency of hrtimer and NMI