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* docs: RCU: Convert stallwarn.txt to ReSTMauro Carvalho Chehab2020-06-291-316/+0
| | | | | | | | | | | | - Add a SPDX header; - Adjust document and section titles; - Fix list markups; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add it to RCU/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
* rcu: Remove kfree_rcu() special casing and lazy-callback handlingJoel Fernandes (Google)2020-01-241-8/+3
| | | | | | | | | | | | | This commit removes kfree_rcu() special-casing and the lazy-callback handling from Tree RCU. It moves some of this special casing to Tiny RCU, the removal of which will be the subject of later commits. This results in a nice negative delta. Suggested-by: Paul E. McKenney <paulmck@linux.ibm.com> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> [ paulmck: Add slab.h #include, thanks to kbuild test robot <lkp@intel.com>. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
* doc: Add rcutree.kthread_prio pointer to stallwarn.txtPaul E. McKenney2019-08-011-0/+6
| | | | | | | | | This commit adds mention of the rcutree.kthread_prio kernel boot parameter to the discussion of how high-priority real-time tasks can result in RCU CPU stall warnings. (However, this does not necessarily help when the high-priority real-time tasks are using dubious deadlines.) Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Fixup definition of rcupdate.rcu_task_stall_timeoutZhenzhong Duan2019-05-281-1/+1
| | | | | | | | A positive value of rcupdate.rcu_task_stall_timeout is an interval in seconds rather than jiffies. Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* rcu: Discard separate per-CPU callback countsPaul E. McKenney2019-01-251-7/+8
| | | | | | | | | | | | | | | | | | Back when there were multiple flavors of RCU, it was necessary to separately count lazy and non-lazy callbacks for each CPU. These counts were used in CONFIG_RCU_FAST_NO_HZ kernels to determine how long a newly idle CPU should be allowed to sleep before handling its RCU callbacks. But now that there is only one flavor, the callback counts for a given CPU's sole rcu_data structure are the counts for that CPU. This commit therefore removes the rcu_data structure's ->nonlazy_posted and ->nonlazy_posted_snap fields, the rcu_idle_count_callbacks_posted() and rcu_cpu_has_callbacks() functions, repurposes the rcu_data structure's ->all_lazy field to record the laziness state at the beginning of the latest idle sojourn, and modifies CONFIG_RCU_FAST_NO_HZ RCU CPU stall warnings accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Correct parameter in stallwarnJoel Fernandes (Google)2018-11-121-1/+1
| | | | | | | | The stallwarn document incorrectly mentions 'fps=' instead of 'fqs='. This commit orrects that. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Remove rcu_preempt_state reference in stallwarnJoel Fernandes (Google)2018-11-081-3/+2
| | | | | | | | | | | Consolidation of RCU-bh, RCU-preempt, and RCU-sched into one RCU flavor to rule them all resulted in the removal of rcu_preempt_state. However, stallwarn.txt still mentions rcu_preempt_state. This commit therefore Updates stallwarn documentation accordingly. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Update removal of RCU-bh/sched update machineryPaul E. McKenney2018-08-301-8/+5
| | | | | | | | | | | | | | | The RCU-bh update API is now defined in terms of that of RCU-bh and RCU-sched, so this commit updates the documentation accordingly. In addition, although RCU-sched persists in !PREEMPT kernels, in the PREEMPT case its update API is now defined in terms of that of RCU-preempt, so this commit also updates the documentation accordingly. While in the area, this commit removes the documentation for the now-obsolete synchronize_rcu_mult() and clarifies the Tasks RCU documentation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Update RCU CPU stall-warning documentationPaul E. McKenney2018-07-121-12/+12
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()Paul E. McKenney2017-12-041-6/+4
| | | | | | | | Now that cond_resched() also provides RCU quiescent states when needed, it can be used in place of cond_resched_rcu_qs(). This commit therefore documents this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Update RCU CPU stall warning messagesPaul E. McKenney2017-10-091-77/+105
| | | | | | | The RCU CPU stall warnings have morphed significantly since the last update, so this commit brings the documentation up to date. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Slow systems can stall RCU grace periodsPaul E. McKenney2017-10-091-0/+6
| | | | | | | | | | | If a fast system has a worst-case grace-period duration of (say) ten seconds, then running the same workload on a system ten times as slow will get you an RCU CPU stall warning given default stall-warning timeout settings. This commit therefore adds this possibility to stallwarn.txt. Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Long-running irq handlers can stall RCU grace periodsPaul E. McKenney2017-10-091-1/+11
| | | | | | | | | | | If a periodic interrupt's handler takes longer to execute than the period between successive interrupts, RCU's kthreads and softirq handlers can be prevented from executing, resulting in otherwise inexplicable RCU CPU stall warnings. This commit therefore calls out this possibility in Documentation/RCU/stallwarn.txt. Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Update stallwarn.txt to make causes more prominentPaul E. McKenney2017-04-121-90/+100
| | | | | | | | This commit rearranges the Documentation/RCU/stallwarn.txt file to put the list of issues that can cause RCU CPU stall warnings near the beginning of the document. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* Documentation: Fix spelling mistakeEric Engestrom2016-06-141-1/+1
| | | | | | Signed-off-by: Eric Engestrom <eric@engestrom.ch> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Call out slow consoles as cause of stall warningsPaul E. McKenney2015-10-061-0/+7
| | | | | | | | | | The Linux kernel outputs copious text during boot, and a slow serial console can result in stall warnings, particularly when messages are printed with interrupts disabled. This commit adds this to the list of causes of RCU CPU stall warning messages. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* documentation: Describe new expedited stall warningsPaul E. McKenney2015-07-171-0/+17
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove CONFIG_RCU_CPU_STALL_INFOPaul E. McKenney2015-07-171-10/+2
| | | | | | | | | The CONFIG_RCU_CPU_STALL_INFO has been default-y for a couple of releases with no complaints, so it is time to eliminate this Kconfig option entirely, so that the long-form RCU CPU stall warnings cannot be disabled. This commit does just that. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*-. Merge branches 'doc.2015.01.07a', 'fixes.2015.01.15a', ↵Paul E. McKenney2015-01-151-0/+14
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'preempt.2015.01.06a', 'srcu.2015.01.06a', 'stall.2015.01.16a' and 'torture.2015.01.11a' into HEAD doc.2015.01.07a: Documentation updates. fixes.2015.01.15a: Miscellaneous fixes. preempt.2015.01.06a: Changes to handling of lists of preempted tasks. srcu.2015.01.06a: SRCU updates. stall.2015.01.16a: RCU CPU stall-warning updates and fixes. torture.2015.01.11a: RCU torture-test updates and fixes.
| | * rcu: Add GP-kthread-starvation checks to CPU stall warningsPaul E. McKenney2015-01-151-0/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | This commit adds a message that is printed if the relevant grace-period kthread has not been able to run for the two seconds preceding the stall warning. (The two seconds is double the maximum interval between successive bouts of quiescent-state forcing.) Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Improve diagnostics for spurious RCU CPU stall warningsPaul E. McKenney2015-01-061-0/+5
| |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current RCU CPU stall warning code will print "Stall ended before state dump start" any time that the stall-warning code is triggered on a CPU that has already reported a quiescent state for the current grace period and if all quiescent states have been reported for the current grace period. However, a true stall can result in these symptoms, for example, by preventing RCU's grace-period kthreads from ever running This commit therefore checks for this condition, reporting the end of the stall only if one of the grace-period counters has actually advanced. Otherwise, it reports the last time that the grace-period kthread made meaningful progress. (In normal situations, the grace-period kthread should make meaningful progress at least every jiffies_till_next_fqs jiffies.) Reported-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Miroslav Benes <mbenes@suse.cz>
* / documentation: Update sysfs path for rcu_cpu_stall_timeoutXie XiuQi2015-01-061-1/+1
|/ | | | | | | | | | | | | | Commit 6bfc09e2327d ("rcu: Provide RCU CPU stall warnings for tiny RCU") moved the rcu_cpu_stall_timeout module parameter from rcutree.c to rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This commit therefore repairs this omission. commit 96224daa16d6 ("documentation: Update sysfs path for rcu_cpu_stall_suppress") updated the path for rcu_cpu_stall_suppress, but failed to update for rcu_cpu_stall_timeout. Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*-. Merge branches 'torture.2014.11.03a', 'cpu.2014.11.03a', 'doc.2014.11.13a', ↵Paul E. McKenney2014-11-131-10/+4
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'fixes.2014.11.13a', 'signal.2014.10.29a' and 'rt.2014.10.29a' into HEAD cpu.2014.11.03a: Changes for per-CPU variables. doc.2014.11.13a: Documentation updates. fixes.2014.11.13a: Miscellaneous fixes. signal.2014.10.29a: Signal changes. rt.2014.10.29a: Real-time changes. torture.2014.11.03a: torture-test changes.
| | * rcu: Remove redundant TREE_PREEMPT_RCU config optionPranith Kumar2014-10-291-4/+4
| |/ |/| | | | | | | | | | | | | | | PREEMPT_RCU and TREE_PREEMPT_RCU serve the same function after TINY_PREEMPT_RCU has been removed. This patch removes TREE_PREEMPT_RCU and uses PREEMPT_RCU config option in its place. Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Remove CONFIG_RCU_CPU_STALL_VERBOSEPaul E. McKenney2014-10-281-6/+0
|/ | | | | | | | | | | The CONFIG_RCU_CPU_STALL_VERBOSE Kconfig parameter causes preemptible RCU's CPU stall warnings to dump out any preempted tasks that are blocking the current RCU grace period. This information is useful, and the default has been CONFIG_RCU_CPU_STALL_VERBOSE=y for some years. It is therefore time for this commit to remove this Kconfig parameter, so that future kernel builds will always act as if CONFIG_RCU_CPU_STALL_VERBOSE=y. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Add verbiage on RCU-tasks stall warning messagesPaul E. McKenney2014-09-071-9/+24
| | | | | | | This commit documents RCU-tasks stall warning messages and also describes when to use the new cond_resched_rcu_qs() API. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Update sysfs path for rcu_cpu_stall_suppressPaul E. McKenney2014-04-291-1/+1
| | | | | | | | | | | Commit 6bfc09e2327d (rcu: Provide RCU CPU stall warnings for tiny RCU) moved the rcu_cpu_stall_suppress module parameter from rcutree.c to rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This commit therefore repairs this omission. Reported-by: Kirill Tkhai <tkhai@yandex.ru> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Update stall-warning documentationPaul E. McKenney2013-09-251-7/+15
| | | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* Merge commit '8700c95adb03' into timers/nohzFrederic Weisbecker2013-05-021-9/+24
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | The full dynticks tree needs the latest RCU and sched upstream updates in order to fix some dependencies. Merge a common upstream merge point that has these updates. Conflicts: include/linux/perf_event.h kernel/rcutree.h kernel/rcutree_plugin.h Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
| * rcu: Add softirq-stall indications to stall-warning messagesPaul E. McKenney2013-03-131-9/+24
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If RCU's softirq handler is prevented from executing, an RCU CPU stall warning can result. Ways to prevent RCU's softirq handler from executing include: (1) CPU spinning with interrupts disabled, (2) infinite loop in some softirq handler, and (3) in -rt kernels, an infinite loop in a set of real-time threads running at priorities higher than that of RCU's softirq handler. Because this situation can be difficult to track down, this commit causes the count of RCU softirq handler invocations to be printed with RCU CPU stall warnings. This information does require some interpretation, as now documented in Documentation/RCU/stallwarn.txt. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>
* | nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMONFrederic Weisbecker2013-04-031-1/+1
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We are planning to convert the dynticks Kconfig options layout into a choice menu. The user must be able to easily pick any of the following implementations: constant periodic tick, idle dynticks, full dynticks. As this implies a mutual exclusion, the two dynticks implementions need to converge on the selection of a common Kconfig option in order to ease the sharing of a common infrastructure. It would thus seem pretty natural to reuse CONFIG_NO_HZ to that end. It already implements all the idle dynticks code and the full dynticks depends on all that code for now. So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ. On the other hand we want to stay backward compatible: if CONFIG_NO_HZ is set in an older config file, we want to enable CONFIG_NO_HZ_IDLE by default. But we can't afford both at the same time or we run into a circular dependency: 1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select CONFIG_NO_HZ 2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE We might be able to support that from Kconfig/Kbuild but it may not be wise to introduce such a confusing behaviour. So to solve this, create a new CONFIG_NO_HZ_COMMON option which gathers the common code between idle and full dynticks (that common code for now is simply the idle dynticks code) and select it from their referring Kconfig. Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ to it for backward compatibility. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
* rcu: Fix CONFIG_RCU_FAST_NO_HZ stall warning messagePaul E. McKenney2012-09-231-8/+8
| | | | | | | | | | | | | The print_cpu_stall_fast_no_hz() function attempts to print -1 when the ->idle_gp_timer is not pending, but unsigned arithmetic causes it to instead print ULONG_MAX, which is 4294967295 on 32-bit systems and 18446744073709551615 on 64-bit systems. Neither of these are the most reader-friendly values, so this commit instead causes "timer not pending" to be printed when ->idle_gp_timer is not pending. Reported-by: Paul Walmsley <paul@pwsan.com> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Update stall-warning documentationPaul E. McKenney2012-02-211-7/+80
| | | | | | | | | | | | Add documentation of CONFIG_RCU_CPU_STALL_VERBOSE, CONFIG_RCU_CPU_STALL_INFO, and RCU_STALL_DELAY_DELTA. Describe multiple stall-warning messages from a single stall, and the timing of the subsequent messages. Add headings. Remove RCU_SECONDS_TILL_STALL_RECHECK because this value is now computed at runtime from RCU_CPU_STALL_TIMEOUT, so that sysfs changes to the timeout value now directly affect the RCU_SECONDS_TILL_STALL_RECHECK value. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add documentation for raw SRCU read-side primitivesPaul E. McKenney2011-12-111-6/+5
| | | | | | | | Update various files in Documentation/RCU to reflect srcu_read_lock_raw() and srcu_read_unlock_raw(). Credit to Peter Zijlstra for suggesting use of the existing _raw suffix instead of the earlier bulkref names. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Document failing tick as cause of RCU CPU stall warningPaul E. McKenney2011-12-111-0/+5
| | | | | | | | | | | One of lclaudio's systems was seeing RCU CPU stall warnings from idle. These turned out to be caused by a bug that stopped scheduling-clock tick interrupts from being sent to a given CPU for several hundred seconds. This commit therefore updates the documentation to call this out as a possible cause for RCU CPU stall warnings. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Remove conditional compilation for RCU CPU stall warningsPaul E. McKenney2011-05-051-10/+13
| | | | | | | | | | | | | | The RCU CPU stall warnings can now be controlled using the rcu_cpu_stall_suppress boot-time parameter or via the same parameter from sysfs. There is therefore no longer any reason to have kernel config parameters for this feature. This commit therefore removes the RCU_CPU_STALL_DETECTOR and RCU_CPU_STALL_DETECTOR_RUNNABLE kernel config parameters. The RCU_CPU_STALL_TIMEOUT parameter remains to allow the timeout to be tuned and the RCU_CPU_STALL_VERBOSE parameter remains to allow task-stall information to be suppressed if desired. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: upgrade stallwarn.txt documentation for CPU-bound RT processesPaul E. McKenney2010-08-231-0/+18
| | | | | | | | | CPU-bound real-time processes can cause RCU CPU stall warnings, and much other trouble as well. Document the fact that they can cause RCU CPU stall warnings. Suggested-by: Darren Hart <dvhltc@us.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: improve the RCU CPU-stall warning documentationPaul E. McKenney2010-05-101-23/+71
| | | | | | | | The existing Documentation/RCU/stallwarn.txt has proven unhelpful, so rework it a bit. In particular, show how to interpret the stall-warning messages. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: 1Q2010 update for RCU documentationPaul E. McKenney2010-01-161-0/+58
Add expedited functions. Review documentation and update obsolete verbiage. Also fix the advice for the RCU CPU-stall kernel configuration parameter, and document RCU CPU-stall warnings. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12635142581866-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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