user/sven/linux.git/Documentation/sysctl/kernel.txt, branch v4.9.5

printk: add kernel parameter to control writes to /dev/kmsg

2016-08-02T23:35:06Z

Add a "printk.devkmsg" kernel command line parameter which controls how userspace writes into /dev/kmsg. It has three options: * ratelimit - ratelimit logging from userspace. * on - unlimited logging from userspace * off - logging from userspace gets ignored The default setting is to ratelimit the messages written to it. This changes the kernel default setting of "on" to "ratelimit" and we do that because we want to keep userspace spamming /dev/kmsg to sane levels. This is especially moot when a small kernel log buffer wraps around and messages get lost. So the ratelimiting setting should be a sane setting where kernel messages should have a bit higher chance of survival from all the spamming. It additionally does not limit logging to /dev/kmsg while the system is booting if we haven't disabled it on the command line. Furthermore, we can control the logging from a lower priority sysctl interface - kernel.printk_devkmsg. That interface will succeed only if printk.devkmsg *hasn't* been supplied on the command line. If it has, then printk.devkmsg is a one-time setting which remains for the duration of the system lifetime. This "locking" of the setting is to prevent userspace from changing the logging on us through sysctl(2). This patch is based on previous patches from Linus and Steven. [bp@suse.de: fixes] Link: http://lkml.kernel.org/r/20160719072344.GC25563@nazgul.tnic Link: http://lkml.kernel.org/r/20160716061745.15795-3-bp@alien8.de Signed-off-by: Borislav Petkov Cc: Dave Young Cc: Franck Bui Cc: Greg Kroah-Hartman Cc: Ingo Molnar Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Uwe Kleine-König Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

rcu: sysctl: Panic on RCU Stall

2016-06-15T23:00:05Z

It is not always easy to determine the cause of an RCU stall just by analysing the RCU stall messages, mainly when the problem is caused by the indirect starvation of rcu threads. For example, when preempt_rcu is not awakened due to the starvation of a timer softirq. We have been hard coding panic() in the RCU stall functions for some time while testing the kernel-rt. But this is not possible in some scenarios, like when supporting customers. This patch implements the sysctl kernel.panic_on_rcu_stall. If set to 1, the system will panic() when an RCU stall takes place, enabling the capture of a vmcore. The vmcore provides a way to analyze all kernel/tasks states, helping out to point to the culprit and the solution for the stall. The kernel.panic_on_rcu_stall sysctl is disabled by default. Changes from v1: - Fixed a typo in the git log - The if(sysctl_panic_on_rcu_stall) panic() is in a static function - Fixed the CONFIG_TINY_RCU compilation issue - The var sysctl_panic_on_rcu_stall is now __read_mostly Cc: Jonathan Corbet Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Acked-by: Christian Borntraeger Reviewed-by: Josh Triplett Reviewed-by: Arnaldo Carvalho de Melo Tested-by: "Luis Claudio R. Goncalves" Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Paul E. McKenney

perf core: Separate accounting of contexts and real addresses in a stack trace

2016-05-17T02:11:53Z

The perf_sample->ip_callchain->nr value includes all the entries in the ip_callchain->ip[] array, real addresses and PERF_CONTEXT_{KERNEL,USER,etc}, while what the user expects is that what is in the kernel.perf_event_max_stack sysctl or in the upcoming per event perf_event_attr.sample_max_stack knob be honoured in terms of IP addresses in the stack trace. So allocate a bunch of extra entries for contexts, and do the accounting via perf_callchain_entry_ctx struct members. A new sysctl, kernel.perf_event_max_contexts_per_stack is also introduced for investigating possible bugs in the callchain implementation by some arch. Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Alexei Starovoitov Cc: Brendan Gregg Cc: David Ahern Cc: Frederic Weisbecker Cc: He Kuang Cc: Jiri Olsa Cc: Masami Hiramatsu Cc: Milian Wolff Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: Wang Nan Cc: Zefan Li Link: http://lkml.kernel.org/n/tip-3b4wnqk340c4sg4gwkfdi9yk@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo

Merge branch 'perf/urgent' into perf/core, to pick up fixes

2016-05-11T14:56:38Z

Signed-off-by: Ingo Molnar

perf/core: Change the default paranoia level to 2

2016-05-10T00:57:12Z

Allowing unprivileged kernel profiling lets any user dump follow kernel control flow and dump kernel registers. This most likely allows trivial kASLR bypassing, and it may allow other mischief as well. (Off the top of my head, the PERF_SAMPLE_REGS_INTR output during /dev/urandom reads could be quite interesting.) Signed-off-by: Andy Lutomirski Acked-by: Kees Cook Signed-off-by: Linus Torvalds

perf core: Allow setting up max frame stack depth via sysctl

2016-04-27T13:20:39Z

The default remains 127, which is good for most cases, and not even hit most of the time, but then for some cases, as reported by Brendan, 1024+ deep frames are appearing on the radar for things like groovy, ruby. And in some workloads putting a _lower_ cap on this may make sense. One that is per event still needs to be put in place tho. The new file is: # cat /proc/sys/kernel/perf_event_max_stack 127 Chaging it: # echo 256 > /proc/sys/kernel/perf_event_max_stack # cat /proc/sys/kernel/perf_event_max_stack 256 But as soon as there is some event using callchains we get: # echo 512 > /proc/sys/kernel/perf_event_max_stack -bash: echo: write error: Device or resource busy # Because we only allocate the callchain percpu data structures when there is a user, which allows for changing the max easily, its just a matter of having no callchain users at that point. Reported-and-Tested-by: Brendan Gregg Reviewed-by: Frederic Weisbecker Acked-by: Alexei Starovoitov Acked-by: David Ahern Cc: Adrian Hunter Cc: Alexander Shishkin Cc: He Kuang Cc: Jiri Olsa Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Milian Wolff Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: Wang Nan Cc: Zefan Li Link: http://lkml.kernel.org/r/20160426002928.GB16708@kernel.org Signed-off-by: Arnaldo Carvalho de Melo

Merge tag 'tty-4.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2016-03-17T20:53:25Z

Pull tty/serial updates from Greg KH: "Here's the big tty/serial driver pull request for 4.6-rc1. Lots of changes in here, Peter has been on a tear again, with lots of refactoring and bugs fixes, many thanks to the great work he has been doing. Lots of driver updates and fixes as well, full details in the shortlog. All have been in linux-next for a while with no reported issues" * tag 'tty-4.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (220 commits) serial: 8250: describe CONFIG_SERIAL_8250_RSA serial: samsung: optimize UART rx fifo access routine serial: pl011: add mark/space parity support serial: sa1100: make sa1100_register_uart_fns a function tty: serial: 8250: add MOXA Smartio MUE boards support serial: 8250: convert drivers to use up_to_u8250p() serial: 8250/mediatek: fix building with SERIAL_8250=m serial: 8250/ingenic: fix building with SERIAL_8250=m serial: 8250/uniphier: fix modular build Revert "drivers/tty/serial: make 8250/8250_ingenic.c explicitly non-modular" Revert "drivers/tty/serial: make 8250/8250_mtk.c explicitly non-modular" serial: mvebu-uart: initial support for Armada-3700 serial port serial: mctrl_gpio: Add missing module license serial: ifx6x60: avoid uninitialized variable use tty/serial: at91: fix bad offset for UART timeout register tty/serial: at91: restore dynamic driver binding serial: 8250: Add hardware dependency to RT288X option TTY, devpts: document pty count limiting tty: goldfish: support platform_device with id -1 drivers: tty: goldfish: Add device tree bindings ...

Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2016-03-15T02:14:06Z

Pull scheduler updates from Ingo Molnar: "The main changes in this cycle are: - Make schedstats a runtime tunable (disabled by default) and optimize it via static keys. As most distributions enable CONFIG_SCHEDSTATS=y due to its instrumentation value, this is a nice performance enhancement. (Mel Gorman) - Implement 'simple waitqueues' (swait): these are just pure waitqueues without any of the more complex features of full-blown waitqueues (callbacks, wake flags, wake keys, etc.). Simple waitqueues have less memory overhead and are faster. Use simple waitqueues in the RCU code (in 4 different places) and for handling KVM vCPU wakeups. (Peter Zijlstra, Daniel Wagner, Thomas Gleixner, Paul Gortmaker, Marcelo Tosatti) - sched/numa enhancements (Rik van Riel) - NOHZ performance enhancements (Rik van Riel) - Various sched/deadline enhancements (Steven Rostedt) - Various fixes (Peter Zijlstra) - ... and a number of other fixes, cleanups and smaller enhancements" * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (29 commits) sched/cputime: Fix steal_account_process_tick() to always return jiffies sched/deadline: Remove dl_new from struct sched_dl_entity Revert "kbuild: Add option to turn incompatible pointer check into error" sched/deadline: Remove superfluous call to switched_to_dl() sched/debug: Fix preempt_disable_ip recording for preempt_disable() sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity time, acct: Drop irq save & restore from __acct_update_integrals() acct, time: Change indentation in __acct_update_integrals() sched, time: Remove non-power-of-two divides from __acct_update_integrals() sched/rt: Kick RT bandwidth timer immediately on start up sched/debug: Add deadline scheduler bandwidth ratio to /proc/sched_debug sched/debug: Move sched_domain_sysctl to debug.c sched/debug: Move the /sys/kernel/debug/sched_features file setup into debug.c sched/rt: Fix PI handling vs. sched_setscheduler() sched/core: Remove duplicated sched_group_set_shares() prototype sched/fair: Consolidate nohz CPU load update code sched/fair: Avoid using decay_load_missed() with a negative value sched/deadline: Always calculate end of period on sched_yield() sched/cgroup: Fix cgroup entity load tracking tear-down rcu: Use simple wait queues where possible in rcutree ...

TTY, devpts: document pty count limiting

2016-03-08T00:11:14Z

Logic has been changed in kernel 3.4 by commit e9aba5158a80 ("tty: rework pty count limiting") but still not documented. Sysctl kernel.pty.max works as global limit, kernel.pty.reserve ptys are reserved for initial devpts instance (mounted without "newinstance"). Per-instance limit also could be set by mount option "max=%d". Signed-off-by: Konstantin Khlebnikov Signed-off-by: Greg Kroah-Hartman

sched/debug: Make schedstats a runtime tunable that is disabled by default

2016-02-09T10:54:23Z

schedstats is very useful during debugging and performance tuning but it incurs overhead to calculate the stats. As such, even though it can be disabled at build time, it is often enabled as the information is useful. This patch adds a kernel command-line and sysctl tunable to enable or disable schedstats on demand (when it's built in). It is disabled by default as someone who knows they need it can also learn to enable it when necessary. The benefits are dependent on how scheduler-intensive the workload is. If it is then the patch reduces the number of cycles spent calculating the stats with a small benefit from reducing the cache footprint of the scheduler. These measurements were taken from a 48-core 2-socket machine with Xeon(R) E5-2670 v3 cpus although they were also tested on a single socket machine 8-core machine with Intel i7-3770 processors. netperf-tcp 4.5.0-rc1 4.5.0-rc1 vanilla nostats-v3r1 Hmean 64 560.45 ( 0.00%) 575.98 ( 2.77%) Hmean 128 766.66 ( 0.00%) 795.79 ( 3.80%) Hmean 256 950.51 ( 0.00%) 981.50 ( 3.26%) Hmean 1024 1433.25 ( 0.00%) 1466.51 ( 2.32%) Hmean 2048 2810.54 ( 0.00%) 2879.75 ( 2.46%) Hmean 3312 4618.18 ( 0.00%) 4682.09 ( 1.38%) Hmean 4096 5306.42 ( 0.00%) 5346.39 ( 0.75%) Hmean 8192 10581.44 ( 0.00%) 10698.15 ( 1.10%) Hmean 16384 18857.70 ( 0.00%) 18937.61 ( 0.42%) Small gains here, UDP_STREAM showed nothing intresting and neither did the TCP_RR tests. The gains on the 8-core machine were very similar. tbench4 4.5.0-rc1 4.5.0-rc1 vanilla nostats-v3r1 Hmean mb/sec-1 500.85 ( 0.00%) 522.43 ( 4.31%) Hmean mb/sec-2 984.66 ( 0.00%) 1018.19 ( 3.41%) Hmean mb/sec-4 1827.91 ( 0.00%) 1847.78 ( 1.09%) Hmean mb/sec-8 3561.36 ( 0.00%) 3611.28 ( 1.40%) Hmean mb/sec-16 5824.52 ( 0.00%) 5929.03 ( 1.79%) Hmean mb/sec-32 10943.10 ( 0.00%) 10802.83 ( -1.28%) Hmean mb/sec-64 15950.81 ( 0.00%) 16211.31 ( 1.63%) Hmean mb/sec-128 15302.17 ( 0.00%) 15445.11 ( 0.93%) Hmean mb/sec-256 14866.18 ( 0.00%) 15088.73 ( 1.50%) Hmean mb/sec-512 15223.31 ( 0.00%) 15373.69 ( 0.99%) Hmean mb/sec-1024 14574.25 ( 0.00%) 14598.02 ( 0.16%) Hmean mb/sec-2048 13569.02 ( 0.00%) 13733.86 ( 1.21%) Hmean mb/sec-3072 12865.98 ( 0.00%) 13209.23 ( 2.67%) Small gains of 2-4% at low thread counts and otherwise flat. The gains on the 8-core machine were slightly different tbench4 on 8-core i7-3770 single socket machine Hmean mb/sec-1 442.59 ( 0.00%) 448.73 ( 1.39%) Hmean mb/sec-2 796.68 ( 0.00%) 794.39 ( -0.29%) Hmean mb/sec-4 1322.52 ( 0.00%) 1343.66 ( 1.60%) Hmean mb/sec-8 2611.65 ( 0.00%) 2694.86 ( 3.19%) Hmean mb/sec-16 2537.07 ( 0.00%) 2609.34 ( 2.85%) Hmean mb/sec-32 2506.02 ( 0.00%) 2578.18 ( 2.88%) Hmean mb/sec-64 2511.06 ( 0.00%) 2569.16 ( 2.31%) Hmean mb/sec-128 2313.38 ( 0.00%) 2395.50 ( 3.55%) Hmean mb/sec-256 2110.04 ( 0.00%) 2177.45 ( 3.19%) Hmean mb/sec-512 2072.51 ( 0.00%) 2053.97 ( -0.89%) In constract, this shows a relatively steady 2-3% gain at higher thread counts. Due to the nature of the patch and the type of workload, it's not a surprise that the result will depend on the CPU used. hackbench-pipes 4.5.0-rc1 4.5.0-rc1 vanilla nostats-v3r1 Amean 1 0.0637 ( 0.00%) 0.0660 ( -3.59%) Amean 4 0.1229 ( 0.00%) 0.1181 ( 3.84%) Amean 7 0.1921 ( 0.00%) 0.1911 ( 0.52%) Amean 12 0.3117 ( 0.00%) 0.2923 ( 6.23%) Amean 21 0.4050 ( 0.00%) 0.3899 ( 3.74%) Amean 30 0.4586 ( 0.00%) 0.4433 ( 3.33%) Amean 48 0.5910 ( 0.00%) 0.5694 ( 3.65%) Amean 79 0.8663 ( 0.00%) 0.8626 ( 0.43%) Amean 110 1.1543 ( 0.00%) 1.1517 ( 0.22%) Amean 141 1.4457 ( 0.00%) 1.4290 ( 1.16%) Amean 172 1.7090 ( 0.00%) 1.6924 ( 0.97%) Amean 192 1.9126 ( 0.00%) 1.9089 ( 0.19%) Some small gains and losses and while the variance data is not included, it's close to the noise. The UMA machine did not show anything particularly different pipetest 4.5.0-rc1 4.5.0-rc1 vanilla nostats-v2r2 Min Time 4.13 ( 0.00%) 3.99 ( 3.39%) 1st-qrtle Time 4.38 ( 0.00%) 4.27 ( 2.51%) 2nd-qrtle Time 4.46 ( 0.00%) 4.39 ( 1.57%) 3rd-qrtle Time 4.56 ( 0.00%) 4.51 ( 1.10%) Max-90% Time 4.67 ( 0.00%) 4.60 ( 1.50%) Max-93% Time 4.71 ( 0.00%) 4.65 ( 1.27%) Max-95% Time 4.74 ( 0.00%) 4.71 ( 0.63%) Max-99% Time 4.88 ( 0.00%) 4.79 ( 1.84%) Max Time 4.93 ( 0.00%) 4.83 ( 2.03%) Mean Time 4.48 ( 0.00%) 4.39 ( 1.91%) Best99%Mean Time 4.47 ( 0.00%) 4.39 ( 1.91%) Best95%Mean Time 4.46 ( 0.00%) 4.38 ( 1.93%) Best90%Mean Time 4.45 ( 0.00%) 4.36 ( 1.98%) Best50%Mean Time 4.36 ( 0.00%) 4.25 ( 2.49%) Best10%Mean Time 4.23 ( 0.00%) 4.10 ( 3.13%) Best5%Mean Time 4.19 ( 0.00%) 4.06 ( 3.20%) Best1%Mean Time 4.13 ( 0.00%) 4.00 ( 3.39%) Small improvement and similar gains were seen on the UMA machine. The gain is small but it stands to reason that doing less work in the scheduler is a good thing. The downside is that the lack of schedstats and tracepoints may be surprising to experts doing performance analysis until they find the existence of the schedstats= parameter or schedstats sysctl. It will be automatically activated for latencytop and sleep profiling to alleviate the problem. For tracepoints, there is a simple warning as it's not safe to activate schedstats in the context when it's known the tracepoint may be wanted but is unavailable. Signed-off-by: Mel Gorman Reviewed-by: Matt Fleming Reviewed-by: Srikar Dronamraju Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1454663316-22048-1-git-send-email-mgorman@techsingularity.net Signed-off-by: Ingo Molnar