--- zzzz-none-000/linux-3.10.107/Documentation/sysctl/kernel.txt 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/Documentation/sysctl/kernel.txt 2021-02-04 17:41:59.000000000 +0000 @@ -33,6 +33,12 @@ - domainname - hostname - hotplug +- hardlockup_all_cpu_backtrace +- hung_task_panic +- hung_task_check_count +- hung_task_timeout_secs +- hung_task_warnings +- kexec_load_disabled - kptr_restrict - kstack_depth_to_print [ X86 only ] - l2cr [ PPC only ] @@ -49,8 +55,9 @@ - overflowuid - panic - panic_on_oops -- panic_on_unrecovered_nmi - panic_on_stackoverflow +- panic_on_unrecovered_nmi +- panic_on_warn - pid_max - powersave-nap [ PPC only ] - printk @@ -70,12 +77,16 @@ - shmall - shmmax [ sysv ipc ] - shmmni -- softlockup_thresh +- 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 ============================================================== @@ -108,10 +119,12 @@ auto_msgmni: -Enables/Disables automatic recomputing of msgmni upon memory add/remove -or upon ipc namespace creation/removal (see the msgmni description -above). Echoing "1" into this file enables msgmni automatic recomputing. -Echoing "0" turns it off. auto_msgmni default value is 1. +This variable has no effect and may be removed in future kernel +releases. Reading it always returns 0. +Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni +upon memory add/remove or upon ipc namespace creation/removal. +Echoing "1" into this file enabled msgmni automatic recomputing. +Echoing "0" turned it off. auto_msgmni default value was 1. ============================================================== @@ -182,8 +195,11 @@ % '%' is dropped %% output one '%' %p pid - %u uid - %g gid + %P global pid (init PID namespace) + %i tid + %I global tid (init PID namespace) + %u uid (in initial user namespace) + %g gid (in initial user namespace) %d dump mode, matches PR_SET_DUMPABLE and /proc/sys/fs/suid_dumpable %s signal number @@ -278,6 +294,17 @@ see the hostname(1) man page. ============================================================== +hardlockup_all_cpu_backtrace: + +This value controls the hard lockup detector behavior when a hard +lockup condition is detected as to whether or not to gather further +debug information. If enabled, arch-specific all-CPU stack dumping +will be initiated. + +0: do nothing. This is the default behavior. + +1: on detection capture more debug information. +============================================================== hotplug: @@ -286,6 +313,58 @@ ============================================================== +hung_task_panic: + +Controls the kernel's behavior when a hung task is detected. +This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. + +0: continue operation. This is the default behavior. + +1: panic immediately. + +============================================================== + +hung_task_check_count: + +The upper bound on the number of tasks that are checked. +This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. + +============================================================== + +hung_task_timeout_secs: + +Check interval. When a task in D state did not get scheduled +for more than this value report a warning. +This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. + +0: means infinite timeout - no checking done. +Possible values to set are in range {0..LONG_MAX/HZ}. + +============================================================== + +hung_task_warnings: + +The maximum number of warnings to report. During a check interval +if a hung task is detected, this value is decreased by 1. +When this value reaches 0, no more warnings will be reported. +This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. + +-1: report an infinite number of warnings. + +============================================================== + +kexec_load_disabled: + +A toggle indicating if the kexec_load syscall has been disabled. This +value defaults to 0 (false: kexec_load enabled), but can be set to 1 +(true: kexec_load disabled). Once true, kexec can no longer be used, and +the toggle cannot be set back to false. This allows a kexec image to be +loaded before disabling the syscall, allowing a system to set up (and +later use) an image without it being altered. Generally used together +with the "modules_disabled" sysctl. + +============================================================== + kptr_restrict: This toggle indicates whether restrictions are placed on @@ -330,7 +409,7 @@ in an otherwise modular kernel. This toggle defaults to off (0), but can be set true (1). Once true, modules can be neither loaded nor unloaded, and the toggle cannot be set back -to false. +to false. Generally used with the "kexec_load_disabled" toggle. ============================================================== @@ -352,16 +431,86 @@ 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. - -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. +This parameter can be used to control the NMI watchdog +(i.e. the hard lockup detector) on x86 systems. + + 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). + +============================================================== + +numa_balancing + +Enables/disables automatic page fault based NUMA memory +balancing. Memory is moved automatically to nodes +that access it often. + +Enables/disables automatic NUMA memory balancing. On NUMA machines, there +is a performance penalty if remote memory is accessed by a CPU. When this +feature is enabled the kernel samples what task thread is accessing memory +by periodically unmapping pages and later trapping a page fault. At the +time of the page fault, it is determined if the data being accessed should +be migrated to a local memory node. + +The unmapping of pages and trapping faults incur additional overhead that +ideally is offset by improved memory locality but there is no universal +guarantee. If the target workload is already bound to NUMA nodes then this +feature should be disabled. Otherwise, if the system overhead from the +feature is too high then the rate the kernel samples for NUMA hinting +faults may be controlled by the numa_balancing_scan_period_min_ms, +numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, +numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls. + +============================================================== + +numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, +numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb + +Automatic NUMA balancing scans tasks address space and unmaps pages to +detect if pages are properly placed or if the data should be migrated to a +memory node local to where the task is running. Every "scan delay" the task +scans the next "scan size" number of pages in its address space. When the +end of the address space is reached the scanner restarts from the beginning. + +In combination, the "scan delay" and "scan size" determine the scan rate. +When "scan delay" decreases, the scan rate increases. The scan delay and +hence the scan rate of every task is adaptive and depends on historical +behaviour. If pages are properly placed then the scan delay increases, +otherwise the scan delay decreases. The "scan size" is not adaptive but +the higher the "scan size", the higher the scan rate. + +Higher scan rates incur higher system overhead as page faults must be +trapped and potentially data must be migrated. However, the higher the scan +rate, the more quickly a tasks memory is migrated to a local node if the +workload pattern changes and minimises performance impact due to remote +memory accesses. These sysctls control the thresholds for scan delays and +the number of pages scanned. + +numa_balancing_scan_period_min_ms is the minimum time in milliseconds to +scan a tasks virtual memory. It effectively controls the maximum scanning +rate for each task. + +numa_balancing_scan_delay_ms is the starting "scan delay" used for a task +when it initially forks. + +numa_balancing_scan_period_max_ms is the maximum time in milliseconds to +scan a tasks virtual memory. It effectively controls the minimum scanning +rate for each task. + +numa_balancing_scan_size_mb is how many megabytes worth of pages are +scanned for a given scan. ============================================================== @@ -402,19 +551,6 @@ ============================================================== -panic_on_unrecovered_nmi: - -The default Linux behaviour on an NMI of either memory or unknown is -to continue operation. For many environments such as scientific -computing it is preferable that the box is taken out and the error -dealt with than an uncorrected parity/ECC error get propagated. - -A small number of systems do generate NMI's for bizarre random reasons -such as power management so the default is off. That sysctl works like -the existing panic controls already in that directory. - -============================================================== - panic_on_oops: Controls the kernel's behaviour when an oops or BUG is encountered. @@ -438,6 +574,30 @@ ============================================================== +panic_on_unrecovered_nmi: + +The default Linux behaviour on an NMI of either memory or unknown is +to continue operation. For many environments such as scientific +computing it is preferable that the box is taken out and the error +dealt with than an uncorrected parity/ECC error get propagated. + +A small number of systems do generate NMI's for bizarre random reasons +such as power management so the default is off. That sysctl works like +the existing panic controls already in that directory. + +============================================================== + +panic_on_warn: + +Calls panic() in the WARN() path when set to 1. This is useful to avoid +a kernel rebuild when attempting to kdump at the location of a WARN(). + +0: only WARN(), default behaviour. + +1: call panic() after printing out WARN() location. + +============================================================== + perf_cpu_time_max_percent: Hints to the kernel how much CPU time it should be allowed to @@ -641,12 +801,55 @@ ============================================================== -softlockup_thresh: +sysctl_writes_strict: + +Control how file position affects the behavior of updating sysctl values +via the /proc/sys interface: + + -1 - Legacy per-write sysctl value handling, with no printk warnings. + Each write syscall must fully contain the sysctl value to be + written, and multiple writes on the same sysctl file descriptor + will rewrite the sysctl value, regardless of file position. + 0 - (default) Same behavior as above, but warn about processes that + perform writes to a sysctl file descriptor when the file position + is not 0. + 1 - Respect file position when writing sysctl strings. Multiple writes + will append to the sysctl value buffer. Anything past the max length + of the sysctl value buffer will be ignored. Writes to numeric sysctl + entries must always be at file position 0 and the value must be + fully contained in the buffer sent in the write syscall. + +============================================================== + +softlockup_all_cpu_backtrace: + +This value controls the soft lockup detector thread's behavior +when a soft lockup condition is detected as to whether or not +to gather further debug information. If enabled, each cpu will +be issued an NMI and instructed to capture stack trace. + +This feature is only applicable for architectures which support +NMI. + +0: do nothing. This is the default behavior. -This value can be used to lower the softlockup tolerance threshold. The -default threshold is 60 seconds. If a cpu is locked up for 60 seconds, -the kernel complains. Valid values are 1-60 seconds. Setting this -tunable to zero will disable the softlockup detection altogether. +1: on detection capture more debug information. + +============================================================== + +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. ============================================================== @@ -674,6 +877,31 @@ 1024 - A module from drivers/staging was loaded. 2048 - The system is working around a severe firmware bug. 4096 - An out-of-tree module has been loaded. +8192 - An unsigned module has been loaded in a kernel supporting module + signature. +16384 - A soft lockup has previously occurred on the system. +32768 - The kernel has been live patched. + +============================================================== + +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. ============================================================== @@ -685,3 +913,56 @@ NMI switch that most IA32 servers have fires unknown NMI up, for 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_cpumask: + +This value can be used to control on which cpus the watchdog may run. +The default cpumask is all possible cores, but if NO_HZ_FULL is +enabled in the kernel config, and cores are specified with the +nohz_full= boot argument, those cores are excluded by default. +Offline cores can be included in this mask, and if the core is later +brought online, the watchdog will be started based on the mask value. + +Typically this value would only be touched in the nohz_full case +to re-enable cores that by default were not running the watchdog, +if a kernel lockup was suspected on those cores. + +The argument value is the standard cpulist format for cpumasks, +so for example to enable the watchdog on cores 0, 2, 3, and 4 you +might say: + + echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask + +============================================================== + +watchdog_thresh: + +This value can be used to control the frequency of hrtimer and NMI +events and the soft and hard lockup thresholds. The default threshold +is 10 seconds. + +The softlockup threshold is (2 * watchdog_thresh). Setting this +tunable to zero will disable lockup detection altogether. + +==============================================================