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2022-03-31Revert "signal, x86: Delay calling signals in atomic on RT enabled kernels"Thomas Gleixner
Revert commit bf9ad37dc8a. It needs to be better encapsulated and generalized. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
2022-03-22Merge tag 'sched-core-2022-03-22' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler updates from Ingo Molnar: - Cleanups for SCHED_DEADLINE - Tracing updates/fixes - CPU Accounting fixes - First wave of changes to optimize the overhead of the scheduler build, from the fast-headers tree - including placeholder *_api.h headers for later header split-ups. - Preempt-dynamic using static_branch() for ARM64 - Isolation housekeeping mask rework; preperatory for further changes - NUMA-balancing: deal with CPU-less nodes - NUMA-balancing: tune systems that have multiple LLC cache domains per node (eg. AMD) - Updates to RSEQ UAPI in preparation for glibc usage - Lots of RSEQ/selftests, for same - Add Suren as PSI co-maintainer * tag 'sched-core-2022-03-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (81 commits) sched/headers: ARM needs asm/paravirt_api_clock.h too sched/numa: Fix boot crash on arm64 systems headers/prep: Fix header to build standalone: <linux/psi.h> sched/headers: Only include <linux/entry-common.h> when CONFIG_GENERIC_ENTRY=y cgroup: Fix suspicious rcu_dereference_check() usage warning sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers sched/topology: Remove redundant variable and fix incorrect type in build_sched_domains sched/deadline,rt: Remove unused parameter from pick_next_[rt|dl]_entity() sched/deadline,rt: Remove unused functions for !CONFIG_SMP sched/deadline: Use __node_2_[pdl|dle]() and rb_first_cached() consistently sched/deadline: Merge dl_task_can_attach() and dl_cpu_busy() sched/deadline: Move bandwidth mgmt and reclaim functions into sched class source file sched/deadline: Remove unused def_dl_bandwidth sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE sched/tracing: Don't re-read p->state when emitting sched_switch event sched/rt: Plug rt_mutex_setprio() vs push_rt_task() race sched/cpuacct: Remove redundant RCU read lock sched/cpuacct: Optimize away RCU read lock sched/cpuacct: Fix charge percpu cpuusage sched/headers: Reorganize, clean up and optimize kernel/sched/sched.h dependencies ...
2022-03-04signal, x86: Delay calling signals in atomic on RT enabled kernelsOleg Nesterov
On x86_64 we must disable preemption before we enable interrupts for stack faults, int3 and debugging, because the current task is using a per CPU debug stack defined by the IST. If we schedule out, another task can come in and use the same stack and cause the stack to be corrupted and crash the kernel on return. When CONFIG_PREEMPT_RT is enabled, spinlock_t locks become sleeping, and one of these is the spin lock used in signal handling. Some of the debug code (int3) causes do_trap() to send a signal. This function calls a spinlock_t lock that has been converted to a sleeping lock. If this happens, the above issues with the corrupted stack is possible. Instead of calling the signal right away, for PREEMPT_RT and x86, the signal information is stored on the stacks task_struct and TIF_NOTIFY_RESUME is set. Then on exit of the trap, the signal resume code will send the signal when preemption is enabled. [ rostedt: Switched from #ifdef CONFIG_PREEMPT_RT to ARCH_RT_DELAYS_SIGNAL_SEND and added comments to the code. ] [bigeasy: Add on 32bit as per Yang Shi, minor rewording. ] [ tglx: Use a config option ] Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/Ygq5aBB/qMQw6aP5@linutronix.de
2022-02-19sched/preempt: Add PREEMPT_DYNAMIC using static keysMark Rutland
Where an architecture selects HAVE_STATIC_CALL but not HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline which will either branch to a callee or return to the caller. On such architectures, a number of constraints can conspire to make those trampolines more complicated and potentially less useful than we'd like. For example: * Hardware and software control flow integrity schemes can require the addition of "landing pad" instructions (e.g. `BTI` for arm64), which will also be present at the "real" callee. * Limited branch ranges can require that trampolines generate or load an address into a register and perform an indirect branch (or at least have a slow path that does so). This loses some of the benefits of having a direct branch. * Interaction with SW CFI schemes can be complicated and fragile, e.g. requiring that we can recognise idiomatic codegen and remove indirections understand, at least until clang proves more helpful mechanisms for dealing with this. For PREEMPT_DYNAMIC, we don't need the full power of static calls, as we really only need to enable/disable specific preemption functions. We can achieve the same effect without a number of the pain points above by using static keys to fold early returns into the preemption functions themselves rather than in an out-of-line trampoline, effectively inlining the trampoline into the start of the function. For arm64, this results in good code generation. For example, the dynamic_cond_resched() wrapper looks as follows when enabled. When disabled, the first `B` is replaced with a `NOP`, resulting in an early return. | <dynamic_cond_resched>: | bti c | b <dynamic_cond_resched+0x10> // or `nop` | mov w0, #0x0 | ret | mrs x0, sp_el0 | ldr x0, [x0, #8] | cbnz x0, <dynamic_cond_resched+0x8> | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret ... compared to the regular form of the function: | <__cond_resched>: | bti c | mrs x0, sp_el0 | ldr x1, [x0, #8] | cbz x1, <__cond_resched+0x18> | mov w0, #0x0 | ret | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret Any architecture which implements static keys should be able to use this to implement PREEMPT_DYNAMIC with similar cost to non-inlined static calls. Since this is likely to have greater overhead than (inlined) static calls, PREEMPT_DYNAMIC is only defaulted to enabled when HAVE_PREEMPT_DYNAMIC_CALL is selected. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20220214165216.2231574-6-mark.rutland@arm.com
2021-11-11preempt: Restore preemption model selection configsValentin Schneider
Commit c597bfddc9e9 ("sched: Provide Kconfig support for default dynamic preempt mode") changed the selectable config names for the preemption model. This means a config file must now select CONFIG_PREEMPT_BEHAVIOUR=y rather than CONFIG_PREEMPT=y to get a preemptible kernel. This means all arch config files would need to be updated - right now they'll all end up with the default CONFIG_PREEMPT_NONE_BEHAVIOUR. Rather than touch a good hundred of config files, restore usage of CONFIG_PREEMPT{_NONE, _VOLUNTARY}. Make them configure: o The build-time preemption model when !PREEMPT_DYNAMIC o The default boot-time preemption model when PREEMPT_DYNAMIC Add siblings of those configs with the _BUILD suffix to unconditionally designate the build-time preemption model (PREEMPT_DYNAMIC is built with the "highest" preemption model it supports, aka PREEMPT). Downstream configs should by now all be depending / selected by CONFIG_PREEMPTION rather than CONFIG_PREEMPT, so only a few sites need patching up. Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Marco Elver <elver@google.com> Link: https://lore.kernel.org/r/20211110202448.4054153-2-valentin.schneider@arm.com
2021-10-05sched: Provide Kconfig support for default dynamic preempt modeFrederic Weisbecker
Currently the boot defined preempt behaviour (aka dynamic preempt) selects full preemption by default when the "preempt=" boot parameter is omitted. However distros may rather want to default to either no preemption or voluntary preemption. To provide with this flexibility, make dynamic preemption a visible Kconfig option and adapt the preemption behaviour selected by the user to either static or dynamic preemption. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210914103134.11309-1-frederic@kernel.org
2021-06-28sched/core: Disable CONFIG_SCHED_CORE by defaultIngo Molnar
This option at minimum adds extra code to the scheduler - even if it's default unused - and most users wouldn't want it. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
2021-06-01sched: Add CONFIG_SCHED_CORE help textPeter Zijlstra
Hugh noted that the SCHED_CORE Kconfig option could do with a help text. Requested-by: Hugh Dickins <hughd@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Hugh Dickins <hughd@google.com> Link: https://lkml.kernel.org/r/YKyhtwhEgvtUDOyl@hirez.programming.kicks-ass.net
2021-05-12sched: Core-wide rq->lockPeter Zijlstra
Introduce the basic infrastructure to have a core wide rq->lock. This relies on the rq->__lock order being in increasing CPU number (inside a core). It is also constrained to SMT8 per lockdep (and SMT256 per preempt_count). Luckily SMT8 is the max supported SMT count for Linux (Mips, Sparc and Power are known to have this). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Don Hiatt <dhiatt@digitalocean.com> Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com> Tested-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/YJUNfzSgptjX7tG6@hirez.programming.kicks-ass.net
2021-02-17preempt: Introduce CONFIG_PREEMPT_DYNAMICMichal Hocko
Preemption mode selection is currently hardcoded on Kconfig choices. Introduce a dedicated option to tune preemption flavour at boot time, This will be only available on architectures efficiently supporting static calls in order not to tempt with the feature against additional overhead that might be prohibitive or undesirable. CONFIG_PREEMPT_DYNAMIC is automatically selected by CONFIG_PREEMPT if the architecture provides the necessary support (CONFIG_STATIC_CALL_INLINE, CONFIG_GENERIC_ENTRY, and provide with __preempt_schedule_function() / __preempt_schedule_notrace_function()). Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> [peterz: relax requirement to HAVE_STATIC_CALL] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210118141223.123667-5-frederic@kernel.org
2019-11-12sched/Kconfig: Fix spelling mistake in user-visible help textSrivatsa S. Bhat (VMware)
Fix a spelling mistake in the help text for PREEMPT_RT. Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/157204450499.10518.4542293884417101528.stgit@srivatsa-ubuntu
2019-07-22sched/rt, Kconfig: Unbreak def/oldconfig with CONFIG_PREEMPT=yThomas Gleixner
The merge of the CONFIG_PREEMPT_RT stub renamed CONFIG_PREEMPT to CONFIG_PREEMPT_LL which causes all defconfigs which have CONFIG_PREEMPT=y set to fall back to CONFIG_PREEMPT_NONE because CONFIG_PREEMPT depends on the preemption mode choice wich defaults to NONE. This also affects oldconfig builds. So rather than changing 114 defconfig files and being an annoyance to users, revert the rename and select a new config symbol PREEMPTION. That keeps everything working smoothly and the revelant ifdef's are going to be fixed up step by step. Reported-by: Mark Rutland <mark.rutland@arm.com> Fixes: a50a3f4b6a31 ("sched/rt, Kconfig: Introduce CONFIG_PREEMPT_RT") Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2019-07-18sched/rt, Kconfig: Introduce CONFIG_PREEMPT_RTThomas Gleixner
Add a new entry to the preemption menu which enables the real-time support for the kernel. The choice is only enabled when an architecture supports it. It selects PREEMPT as the RT features depend on it. To achieve that the existing PREEMPT choice is renamed to PREEMPT_LL which select PREEMPT as well. No functional change. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Acked-by: Clark Williams <williams@redhat.com> Acked-by: Daniel Bristot de Oliveira <bristot@redhat.com> Acked-by: Frederic Weisbecker <frederic@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Acked-by: Daniel Wagner <wagi@monom.org> Acked-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> Acked-by: Julia Cartwright <julia@ni.com> Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com> Acked-by: Gratian Crisan <gratian.crisan@ni.com> Acked-by: Sebastian Siewior <bigeasy@linutronix.de> Cc: Andrew Morton <akpm@linuxfoundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1907172200190.1778@nanos.tec.linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-05-21treewide: Add SPDX license identifier - Makefile/KconfigThomas Gleixner
Add SPDX license identifiers to all Make/Kconfig files which: - Have no license information of any form These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-12-15kconfig: warn no new line at end of fileMasahiro Yamada
It would be nice to warn if a new line is missing at end of file. We could do this by checkpatch.pl for arbitrary files, but new line is rather essential as a statement terminator in Kconfig. The warning message looks like this: kernel/Kconfig.preempt:60:warning: no new line at end of file Currently, kernel/Kconfig.preempt is the only file with no new line at end of file. Fix it. I know there are some false negative cases. For example, no warning is displayed when the last line contains some whitespaces/comments, but no new line. Yet, this commit works well for most cases. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2018-08-02kconfig: include kernel/Kconfig.preempt from init/KconfigChristoph Hellwig
Almost all architectures include it. Add a ARCH_NO_PREEMPT symbol to disable preempt support for alpha, hexagon, non-coldfire m68k and user mode Linux. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2012-03-23locking/kconfig: Simplify INLINE_SPIN_UNLOCK usageRaghavendra K T
Get rid of INLINE_SPIN_UNLOCK entirely replacing it with UNINLINE_SPIN_UNLOCK instead of the reverse meaning. Whoever wants to change the default spinlock inlining behavior and uninline the spinlocks for some weird reason, such as spinlock debugging, paravirt etc. can now all just select UNINLINE_SPIN_UNLOCK Original discussion at: https://lkml.org/lkml/2012/3/21/357 Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Chris Zankel <chris@zankel.net> Cc: linux-mips@linux-mips.org Link: http://lkml.kernel.org/r/20120322095502.30866.75756.sendpatchset@codeblue [ tidied up the changelog a bit ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
2011-06-10sched: Isolate preempt counting in its own config optionFrederic Weisbecker
Create a new CONFIG_PREEMPT_COUNT that handles the inc/dec of preempt count offset independently. So that the offset can be updated by preempt_disable() and preempt_enable() even without the need for CONFIG_PREEMPT beeing set. This prepares to make CONFIG_DEBUG_SPINLOCK_SLEEP working with !CONFIG_PREEMPT where it currently doesn't detect code that sleeps inside explicit preemption disabled sections. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
2008-12-25rcu: provide RCU options on non-preempt architectures tooIngo Molnar
Impact: build fix Some old architectures still do not use kernel/Kconfig.preempt, so the moving of the RCU options there broke their build: In file included from /home/mingo/tip/include/linux/sem.h:81, from /home/mingo/tip/include/linux/sched.h:69, from /home/mingo/tip/arch/alpha/kernel/asm-offsets.c:9: /home/mingo/tip/include/linux/rcupdate.h:62:2: error: #error "Unknown RCU implementation specified to kernel configuration" Move these options back to init/Kconfig, which every architecture includes. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-12-18"Tree RCU": scalable classic RCU implementationPaul E. McKenney
This patch fixes a long-standing performance bug in classic RCU that results in massive internal-to-RCU lock contention on systems with more than a few hundred CPUs. Although this patch creates a separate flavor of RCU for ease of review and patch maintenance, it is intended to replace classic RCU. This patch still handles stress better than does mainline, so I am still calling it ready for inclusion. This patch is against the -tip tree. Nevertheless, experience on an actual 1000+ CPU machine would still be most welcome. Most of the changes noted below were found while creating an rcutiny (which should permit ejecting the current rcuclassic) and while doing detailed line-by-line documentation. Updates from v9 (http://lkml.org/lkml/2008/12/2/334): o Fixes from remainder of line-by-line code walkthrough, including comment spelling, initialization, undesirable narrowing due to type conversion, removing redundant memory barriers, removing redundant local-variable initialization, and removing redundant local variables. I do not believe that any of these fixes address the CPU-hotplug issues that Andi Kleen was seeing, but please do give it a whirl in case the machine is smarter than I am. A writeup from the walkthrough may be found at the following URL, in case you are suffering from terminal insomnia or masochism: http://www.kernel.org/pub/linux/kernel/people/paulmck/tmp/rcutree-walkthrough.2008.12.16a.pdf o Made rcutree tracing use seq_file, as suggested some time ago by Lai Jiangshan. o Added a .csv variant of the rcudata debugfs trace file, to allow people having thousands of CPUs to drop the data into a spreadsheet. Tested with oocalc and gnumeric. Updated documentation to suit. Updates from v8 (http://lkml.org/lkml/2008/11/15/139): o Fix a theoretical race between grace-period initialization and force_quiescent_state() that could occur if more than three jiffies were required to carry out the grace-period initialization. Which it might, if you had enough CPUs. o Apply Ingo's printk-standardization patch. o Substitute local variables for repeated accesses to global variables. o Fix comment misspellings and redundant (but harmless) increments of ->n_rcu_pending (this latter after having explicitly added it). o Apply checkpatch fixes. Updates from v7 (http://lkml.org/lkml/2008/10/10/291): o Fixed a number of problems noted by Gautham Shenoy, including the cpu-stall-detection bug that he was having difficulty convincing me was real. ;-) o Changed cpu-stall detection to wait for ten seconds rather than three in order to reduce false positive, as suggested by Ingo Molnar. o Produced a design document (http://lwn.net/Articles/305782/). The act of writing this document uncovered a number of both theoretical and "here and now" bugs as noted below. o Fix dynticks_nesting accounting confusion, simplify WARN_ON() condition, fix kerneldoc comments, and add memory barriers in dynticks interface functions. o Add more data to tracing. o Remove unused "rcu_barrier" field from rcu_data structure. o Count calls to rcu_pending() from scheduling-clock interrupt to use as a surrogate timebase should jiffies stop counting. o Fix a theoretical race between force_quiescent_state() and grace-period initialization. Yes, initialization does have to go on for some jiffies for this race to occur, but given enough CPUs... Updates from v6 (http://lkml.org/lkml/2008/9/23/448): o Fix a number of checkpatch.pl complaints. o Apply review comments from Ingo Molnar and Lai Jiangshan on the stall-detection code. o Fix several bugs in !CONFIG_SMP builds. o Fix a misspelled config-parameter name so that RCU now announces at boot time if stall detection is configured. o Run tests on numerous combinations of configurations parameters, which after the fixes above, now build and run correctly. Updates from v5 (http://lkml.org/lkml/2008/9/15/92, bad subject line): o Fix a compiler error in the !CONFIG_FANOUT_EXACT case (blew a changeset some time ago, and finally got around to retesting this option). o Fix some tracing bugs in rcupreempt that caused incorrect totals to be printed. o I now test with a more brutal random-selection online/offline script (attached). Probably more brutal than it needs to be on the people reading it as well, but so it goes. o A number of optimizations and usability improvements: o Make rcu_pending() ignore the grace-period timeout when there is no grace period in progress. o Make force_quiescent_state() avoid going for a global lock in the case where there is no grace period in progress. o Rearrange struct fields to improve struct layout. o Make call_rcu() initiate a grace period if RCU was idle, rather than waiting for the next scheduling clock interrupt. o Invoke rcu_irq_enter() and rcu_irq_exit() only when idle, as suggested by Andi Kleen. I still don't completely trust this change, and might back it out. o Make CONFIG_RCU_TRACE be the single config variable manipulated for all forms of RCU, instead of the prior confusion. o Document tracing files and formats for both rcupreempt and rcutree. Updates from v4 for those missing v5 given its bad subject line: o Separated dynticks interface so that NMIs and irqs call separate functions, greatly simplifying it. In particular, this code no longer requires a proof of correctness. ;-) o Separated dynticks state out into its own per-CPU structure, avoiding the duplicated accounting. o The case where a dynticks-idle CPU runs an irq handler that invokes call_rcu() is now correctly handled, forcing that CPU out of dynticks-idle mode. o Review comments have been applied (thank you all!!!). For but one example, fixed the dynticks-ordering issue that Manfred pointed out, saving me much debugging. ;-) o Adjusted rcuclassic and rcupreempt to handle dynticks changes. Attached is an updated patch to Classic RCU that applies a hierarchy, greatly reducing the contention on the top-level lock for large machines. This passes 10-hour concurrent rcutorture and online-offline testing on 128-CPU ppc64 without dynticks enabled, and exposes some timekeeping bugs in presence of dynticks (exciting working on a system where "sleep 1" hangs until interrupted...), which were fixed in the 2.6.27 kernel. It is getting more reliable than mainline by some measures, so the next version will be against -tip for inclusion. See also Manfred Spraul's recent patches (or his earlier work from 2004 at http://marc.info/?l=linux-kernel&m=108546384711797&w=2). We will converge onto a common patch in the fullness of time, but are currently exploring different regions of the design space. That said, I have already gratefully stolen quite a few of Manfred's ideas. This patch provides CONFIG_RCU_FANOUT, which controls the bushiness of the RCU hierarchy. Defaults to 32 on 32-bit machines and 64 on 64-bit machines. If CONFIG_NR_CPUS is less than CONFIG_RCU_FANOUT, there is no hierarchy. By default, the RCU initialization code will adjust CONFIG_RCU_FANOUT to balance the hierarchy, so strongly NUMA architectures may choose to set CONFIG_RCU_FANOUT_EXACT to disable this balancing, allowing the hierarchy to be exactly aligned to the underlying hardware. Up to two levels of hierarchy are permitted (in addition to the root node), allowing up to 16,384 CPUs on 32-bit systems and up to 262,144 CPUs on 64-bit systems. I just know that I am going to regret saying this, but this seems more than sufficient for the foreseeable future. (Some architectures might wish to set CONFIG_RCU_FANOUT=4, which would limit such architectures to 64 CPUs. If this becomes a real problem, additional levels can be added, but I doubt that it will make a significant difference on real hardware.) In the common case, a given CPU will manipulate its private rcu_data structure and the rcu_node structure that it shares with its immediate neighbors. This can reduce both lock and memory contention by multiple orders of magnitude, which should eliminate the need for the strange manipulations that are reported to be required when running Linux on very large systems. Some shortcomings: o More bugs will probably surface as a result of an ongoing line-by-line code inspection. Patches will be provided as required. o There are probably hangs, rcutorture failures, &c. Seems quite stable on a 128-CPU machine, but that is kind of small compared to 4096 CPUs. However, seems to do better than mainline. Patches will be provided as required. o The memory footprint of this version is several KB larger than rcuclassic. A separate UP-only rcutiny patch will be provided, which will reduce the memory footprint significantly, even compared to the old rcuclassic. One such patch passes light testing, and has a memory footprint smaller even than rcuclassic. Initial reaction from various embedded guys was "it is not worth it", so am putting it aside. Credits: o Manfred Spraul for ideas, review comments, and bugs spotted, as well as some good friendly competition. ;-) o Josh Triplett, Ingo Molnar, Peter Zijlstra, Mathieu Desnoyers, Lai Jiangshan, Andi Kleen, Andy Whitcroft, and Andrew Morton for reviews and comments. o Thomas Gleixner for much-needed help with some timer issues (see patches below). o Jon M. Tollefson, Tim Pepper, Andrew Theurer, Jose R. Santos, Andy Whitcroft, Darrick Wong, Nishanth Aravamudan, Anton Blanchard, Dave Kleikamp, and Nathan Lynch for keeping machines alive despite my heavy abuse^Wtesting. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-10rcu: move PREEMPT_RCU config option back under PREEMPTPaul E. McKenney
The original preemptible-RCU patch put the choice between classic and preemptible RCU into kernel/Kconfig.preempt, which resulted in build failures on machines not supporting CONFIG_PREEMPT. This choice was therefore moved to init/Kconfig, which worked, but placed the choice between classic and preemptible RCU at the top level, a very obtuse choice indeed. This patch changes from the Kconfig "choice" mechanism to a pair of booleans, only one of which (CONFIG_PREEMPT_RCU) is user-visible, and is located in kernel/Kconfig.preempt, where one would expect it to be. The other (CONFIG_CLASSIC_RCU) is in init/Kconfig so that it is available to all architectures, hopefully avoiding build breakage. Thanks to Roman Zippel for suggesting this approach. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Dipankar Sarma <dipankar@in.ibm.com> Cc: Josh Triplett <josh@freedesktop.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-01-25sched: remove the !PREEMPT_BKL codeIngo Molnar
remove the !PREEMPT_BKL code. this removes 160 lines of legacy code. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25sched: make PREEMPT_BKL the defaultIngo Molnar
make PREEMPT_BKL the default. precursor to removal of the !PREEMPT_BKL code. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25Preempt-RCU: implementationPaul E. McKenney
This patch implements a new version of RCU which allows its read-side critical sections to be preempted. It uses a set of counter pairs to keep track of the read-side critical sections and flips them when all tasks exit read-side critical section. The details of this implementation can be found in this paper - http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf and the article- http://lwn.net/Articles/253651/ This patch was developed as a part of the -rt kernel development and meant to provide better latencies when read-side critical sections of RCU don't disable preemption. As a consequence of keeping track of RCU readers, the readers have a slight overhead (optimizations in the paper). This implementation co-exists with the "classic" RCU implementations and can be switched to at compiler. Also includes RCU tracing summarized in debugfs. [ akpm@linux-foundation.org: build fixes on non-preempt architectures ] Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Reviewed-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-17Move PREEMPT_NOTIFIERS into an always-included KconfigAvi Kivity
Kconfig.preempt is not included on some archs (for example, m68k). On those archs, the Kconfig machinery complains that KVM selects an undefined symbol PREEMPT_NOTIFIERS (which lives in Kconfig.preempt). So move the offending symbol into a Kconfig file which is included by everyone. Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Avi Kivity <avi@qumranet.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-26[PATCH] sched: arch preempt notifier mechanismAvi Kivity
This adds a general mechanism whereby a task can request the scheduler to notify it whenever it is preempted or scheduled back in. This allows the task to swap any special-purpose registers like the fpu or Intel's VT registers. Signed-off-by: Avi Kivity <avi@qumranet.com> [ mingo@elte.hu: fixes, cleanups ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-05-09Fix trivial typos in Kconfig* filesDavid Sterba
Fix several typos in help text in Kconfig* files. Signed-off-by: David Sterba <dave@jikos.cz> Signed-off-by: Adrian Bunk <bunk@stusta.de>
2005-06-25[PATCH] sched: voluntary kernel preemptionIngo Molnar
This patch adds a new preemption model: 'Voluntary Kernel Preemption'. The 3 models can be selected from a new menu: (X) No Forced Preemption (Server) ( ) Voluntary Kernel Preemption (Desktop) ( ) Preemptible Kernel (Low-Latency Desktop) we still default to the stock (Server) preemption model. Voluntary preemption works by adding a cond_resched() (reschedule-if-needed) call to every might_sleep() check. It is lighter than CONFIG_PREEMPT - at the cost of not having as tight latencies. It represents a different latency/complexity/overhead tradeoff. It has no runtime impact at all if disabled. Here are size stats that show how the various preemption models impact the kernel's size: text data bss dec hex filename 3618774 547184 179896 4345854 424ffe vmlinux.stock 3626406 547184 179896 4353486 426dce vmlinux.voluntary +0.2% 3748414 548640 179896 4476950 445016 vmlinux.preempt +3.5% voluntary-preempt is +0.2% of .text, preempt is +3.5%. This feature has been tested for many months by lots of people (and it's also included in the RHEL4 distribution and earlier variants were in Fedora as well), and it's intended for users and distributions who dont want to use full-blown CONFIG_PREEMPT for one reason or another. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-25[PATCH] enable PREEMPT_BKL on !PREEMPT+SMP tooIngo Molnar
The only sane way to clean up the current 3 lock_kernel() variants seems to be to remove the spinlock-based BKL implementations altogether, and to keep the semaphore-based one only. If we dont want to do that for whatever reason then i'm afraid we have to live with the current complexity. (but i'm open for other cleanup suggestions as well.) To explore this possibility we'll (at a minimum) have to know whether the semaphore-based BKL works fine on plain SMP too. The patch below enables this. The patch may make sense in isolation as well, as it might bring performance benefits: code that would formerly spin on the BKL spinlock will now schedule away and give up the CPU. It might introduce performance regressions as well, if any performance-critical code uses the BKL heavily and gets overscheduled due to the semaphore. I very much hope there is no such performance-critical codepath left though. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-25[PATCH] consolidate PREEMPT options into kernel/Kconfig.preemptIngo Molnar
This patch consolidates the CONFIG_PREEMPT and CONFIG_PREEMPT_BKL preemption options into kernel/Kconfig.preempt. This, besides reducing source-code, also enables more centralized tweaking of preemption related options. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>