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* Working versionNamhoon Kim2015-03-02
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* Protect LITMUS^RT tasks from re-nicingBjoern Brandenburg2014-10-21
| | | | | Assigning a nice value to LITMUS^RT tasks is meaningless. Bail out early.
* Don't call set_tsk_need_resched() on remote LITMUS^RT taskBjoern Brandenburg2014-10-21
| | | | | This patch fixes a BUG_ON() in litmus/preempt.c:33 reported by Felipe Cerqueira & Manohar Vanga.
* Hook into rt scheduling class to protect LITMUS^RT tasksBjoern Brandenburg2014-10-21
| | | | | | The rt scheduling class thinks it's the highest-priority scheduling class around. It is not in LITMUS^RT. Don't go preempting remote cores that run SCHED_LITMUS tasks.
* Don't trigger load balancer in scheduler tick for LITMUS^RTBjoern Brandenburg2014-10-21
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* Cache 'prev' in LITMUS^RT runqueueBjoern Brandenburg2014-10-21
| | | | | | LITMUS^RT plugins like to know who 'prev' is. pick_next_task() doesn't expose that info, so we just cache prev in the runqueue. Could robably be replaced by looking at 'current' instead.
* Hook into finish_switch()Bjoern Brandenburg2014-10-21
| | | | To keep track of stack usage and to notify plugin, if necessary.
* Reset SCHED_LITMUS scheduling class on forkBjoern Brandenburg2014-10-21
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* Block sched_setaffinity() for SCHED_LITMUS tasksBjoern Brandenburg2014-10-21
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* Integrate LITMUS^RT scheduling class with sched_setschedulerBjoern Brandenburg2014-10-21
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* Disable cut-to-CFS optimization in Linux schedulerBjoern Brandenburg2014-10-21
| | | | | Global plugins require that the plugin be called even if there currently is no real-time task executing on the local core.
* Integrate LITMUS^RT with try_to_wake_up() pathBjoern Brandenburg2014-10-21
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* Make LITMUS^RT scheduling class the highest-priority scheduling classBjoern Brandenburg2014-10-21
| | | | | | Needs to be above stop_machine_class for legacy reasons; the main plugins were developed before stop_machine_class was introduced and assume that they are the highest-priority scheduling class.
* Add LITMUS^RT scheduling class in kernel/sched/MakefileBjoern Brandenburg2014-10-21
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* Introduce LITMUS^RT runqueue dummy into struct rqBjoern Brandenburg2014-10-21
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* Integrate SRP ceiling blocking callback with Linux schedulerBjoern Brandenburg2014-10-21
| | | | Check whether a suspension is required at end of schedule().
* Hookup sched_trace_XXX() tracing in Linux schedulerBjoern Brandenburg2014-10-21
| | | | This patch adds context switch tracing to the main Linux scheduler.
* Call sched_state_task_picked() from pick_next_task_stop()Bjoern Brandenburg2014-10-21
| | | | | Otherwise, the scheduler state machine becomes confused (and goes into a rescheduling loop) when stop-machine is triggered.
* Integrate preemption state machine with Linux schedulerBjoern Brandenburg2014-10-21
| | | | Track when a processor is going to schedule "soon".
* Add LITMUS^RT core implementationBjoern Brandenburg2014-10-21
| | | | | | | | | | | | | This patch adds the core of LITMUS^RT: - library functionality (heaps, rt_domain, prioritization, etc.) - budget enforcement logic - job management - system call backends - virtual devices (control page, etc.) - scheduler plugin API (and dummy plugin) This code compiles, but is not yet integrated with the rest of Linux.
* Add SCHED, SCHED2, TICK, and CXS overhead tracepointsBjoern Brandenburg2014-10-21
| | | | | | | This patch integrates the overhead tracepoints into the Linux scheduler that are compatible with plain vanilla Linux (i.e., not specific to LITMUS^RT plugins). This can be used to measure the overheads of an otherwise unmodified kernel.
* Integrate ft_irq_fired() with LinuxBjoern Brandenburg2014-10-21
| | | | | This patch hooks up Feather-Trace's ft_irq_fired() handler with Linux's interrupt handling infrastructure.
* sched: Guarantee new group-entities always have weightPaul Turner2014-01-15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit 0ac9b1c21874d2490331233b3242085f8151e166 upstream. Currently, group entity load-weights are initialized to zero. This admits some races with respect to the first time they are re-weighted in earlty use. ( Let g[x] denote the se for "g" on cpu "x". ) Suppose that we have root->a and that a enters a throttled state, immediately followed by a[0]->t1 (the only task running on cpu[0]) blocking: put_prev_task(group_cfs_rq(a[0]), t1) put_prev_entity(..., t1) check_cfs_rq_runtime(group_cfs_rq(a[0])) throttle_cfs_rq(group_cfs_rq(a[0])) Then, before unthrottling occurs, let a[0]->b[0]->t2 wake for the first time: enqueue_task_fair(rq[0], t2) enqueue_entity(group_cfs_rq(b[0]), t2) enqueue_entity_load_avg(group_cfs_rq(b[0]), t2) account_entity_enqueue(group_cfs_ra(b[0]), t2) update_cfs_shares(group_cfs_rq(b[0])) < skipped because b is part of a throttled hierarchy > enqueue_entity(group_cfs_rq(a[0]), b[0]) ... We now have b[0] enqueued, yet group_cfs_rq(a[0])->load.weight == 0 which violates invariants in several code-paths. Eliminate the possibility of this by initializing group entity weight. Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20131016181627.22647.47543.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: Fix hrtimer_cancel()/rq->lock deadlockBen Segall2014-01-15
| | | | | | | | | | | | | | | | | | | | | | | commit 927b54fccbf04207ec92f669dce6806848cbec7d upstream. __start_cfs_bandwidth calls hrtimer_cancel while holding rq->lock, waiting for the hrtimer to finish. However, if sched_cfs_period_timer runs for another loop iteration, the hrtimer can attempt to take rq->lock, resulting in deadlock. Fix this by ensuring that cfs_b->timer_active is cleared only if the _latest_ call to do_sched_cfs_period_timer is returning as idle. Then __start_cfs_bandwidth can just call hrtimer_try_to_cancel and wait for that to succeed or timer_active == 1. Signed-off-by: Ben Segall <bsegall@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181622.22647.16643.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: Fix cfs_bandwidth misuse of hrtimer_expires_remainingBen Segall2014-01-15
| | | | | | | | | | | | | | | | | commit db06e78cc13d70f10877e0557becc88ab3ad2be8 upstream. hrtimer_expires_remaining does not take internal hrtimer locks and thus must be guarded against concurrent __hrtimer_start_range_ns (but returning HRTIMER_RESTART is safe). Use cfs_b->lock to make it safe. Signed-off-by: Ben Segall <bsegall@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181617.22647.73829.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: Fix race on toggling cfs_bandwidth_usedBen Segall2014-01-15
| | | | | | | | | | | | | | | | | | | | | | | | | commit 1ee14e6c8cddeeb8a490d7b54cd9016e4bb900b4 upstream. When we transition cfs_bandwidth_used to false, any currently throttled groups will incorrectly return false from cfs_rq_throttled. While tg_set_cfs_bandwidth will unthrottle them eventually, currently running code (including at least dequeue_task_fair and distribute_cfs_runtime) will cause errors. Fix this by turning off cfs_bandwidth_used only after unthrottling all cfs_rqs. Tested: toggle bandwidth back and forth on a loaded cgroup. Caused crashes in minutes without the patch, hasn't crashed with it. Signed-off-by: Ben Segall <bsegall@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181611.22647.80365.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: fix the theoretical signal_wake_up() vs schedule() raceOleg Nesterov2014-01-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit e0acd0a68ec7dbf6b7a81a87a867ebd7ac9b76c4 upstream. This is only theoretical, but after try_to_wake_up(p) was changed to check p->state under p->pi_lock the code like __set_current_state(TASK_INTERRUPTIBLE); schedule(); can miss a signal. This is the special case of wait-for-condition, it relies on try_to_wake_up/schedule interaction and thus it does not need mb() between __set_current_state() and if(signal_pending). However, this __set_current_state() can move into the critical section protected by rq->lock, now that try_to_wake_up() takes another lock we need to ensure that it can't be reordered with "if (signal_pending(current))" check inside that section. The patch is actually one-liner, it simply adds smp_wmb() before spin_lock_irq(rq->lock). This is what try_to_wake_up() already does by the same reason. We turn this wmb() into the new helper, smp_mb__before_spinlock(), for better documentation and to allow the architectures to change the default implementation. While at it, kill smp_mb__after_lock(), it has no callers. Perhaps we can also add smp_mb__before/after_spinunlock() for prepare_to_wait(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entitiesKirill Tkhai2014-01-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | commit 757dfcaa41844595964f1220f1d33182dae49976 upstream. This patch touches the RT group scheduling case. Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority, while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because changing of priority on a child level does not guarantee that the priority is the highest all over the rq. So, this leak makes RT balancing unusable. The short example: the task having the highest priority among all rq's RT tasks (no one other task has the same priority) are waking on a throttle rt_rq. The rq's cpupri is set to the task's priority equivalent, but real rq->rt.highest_prio.curr is less. The patch below fixes the problem. Signed-off-by: Kirill Tkhai <tkhai@yandex.ru> Signed-off-by: Peter Zijlstra <peterz@infradead.org> CC: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/49231385567953@web4m.yandex.ru Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: numa: skip inaccessible VMAsMel Gorman2014-01-09
| | | | | | | | | | | | | | commit 3c67f474558748b604e247d92b55dfe89654c81d upstream. Inaccessible VMA should not be trapping NUMA hint faults. Skip them. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Alex Thorlton <athorlton@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: Avoid throttle_cfs_rq() racing with period_timer stoppingBen Segall2013-12-20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit f9f9ffc237dd924f048204e8799da74f9ecf40cf upstream. throttle_cfs_rq() doesn't check to make sure that period_timer is running, and while update_curr/assign_cfs_runtime does, a concurrently running period_timer on another cpu could cancel itself between this cpu's update_curr and throttle_cfs_rq(). If there are no other cfs_rqs running in the tg to restart the timer, this causes the cfs_rq to be stranded forever. Fix this by calling __start_cfs_bandwidth() in throttle if the timer is inactive. (Also add some sched_debug lines for cfs_bandwidth.) Tested: make a run/sleep task in a cgroup, loop switching the cgroup between 1ms/100ms quota and unlimited, checking for timer_active=0 and throttled=1 as a failure. With the throttle_cfs_rq() change commented out this fails, with the full patch it passes. Signed-off-by: Ben Segall <bsegall@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched/fair: Fix small race where child->se.parent,cfs_rq might point to ↵Daisuke Nishimura2013-10-01
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | invalid ones commit 6c9a27f5da9609fca46cb2b183724531b48f71ad upstream. There is a small race between copy_process() and cgroup_attach_task() where child->se.parent,cfs_rq points to invalid (old) ones. parent doing fork() | someone moving the parent to another cgroup -------------------------------+--------------------------------------------- copy_process() + dup_task_struct() -> parent->se is copied to child->se. se.parent,cfs_rq of them point to old ones. cgroup_attach_task() + cgroup_task_migrate() -> parent->cgroup is updated. + cpu_cgroup_attach() + sched_move_task() + task_move_group_fair() +- set_task_rq() -> se.parent,cfs_rq of parent are updated. + cgroup_fork() -> parent->cgroup is copied to child->cgroup. (*1) + sched_fork() + task_fork_fair() -> se.parent,cfs_rq of child are accessed while they point to old ones. (*2) In the worst case, this bug can lead to "use-after-free" and cause a panic, because it's new cgroup's refcount that is incremented at (*1), so the old cgroup(and related data) can be freed before (*2). In fact, a panic caused by this bug was originally caught in RHEL6.4. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff81051e3e>] sched_slice+0x6e/0xa0 [...] Call Trace: [<ffffffff81051f25>] place_entity+0x75/0xa0 [<ffffffff81056a3a>] task_fork_fair+0xaa/0x160 [<ffffffff81063c0b>] sched_fork+0x6b/0x140 [<ffffffff8106c3c2>] copy_process+0x5b2/0x1450 [<ffffffff81063b49>] ? wake_up_new_task+0xd9/0x130 [<ffffffff8106d2f4>] do_fork+0x94/0x460 [<ffffffff81072a9e>] ? sys_wait4+0xae/0x100 [<ffffffff81009598>] sys_clone+0x28/0x30 [<ffffffff8100b393>] stub_clone+0x13/0x20 [<ffffffff8100b072>] ? system_call_fastpath+0x16/0x1b Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/039601ceae06$733d3130$59b79390$@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched/cputime: Do not scale when utime == 0Stanislaw Gruszka2013-10-01
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit 5a8e01f8fa51f5cbce8f37acc050eb2319d12956 upstream. scale_stime() silently assumes that stime < rtime, otherwise when stime == rtime and both values are big enough (operations on them do not fit in 32 bits), the resulting scaling stime can be bigger than rtime. In consequence utime = rtime - stime results in negative value. User space visible symptoms of the bug are overflowed TIME values on ps/top, for example: $ ps aux | grep rcu root 8 0.0 0.0 0 0 ? S 12:42 0:00 [rcuc/0] root 9 0.0 0.0 0 0 ? S 12:42 0:00 [rcub/0] root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] root 11 0.1 0.0 0 0 ? S 12:42 0:02 [rcuop/0] root 12 62422329 0.0 0 0 ? S 12:42 21114581:35 [rcuop/1] root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] or overflowed utime values read directly from /proc/$PID/stat Reference: https://lkml.org/lkml/2013/8/20/259 Reported-and-tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: stable@vger.kernel.org Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Borislav Petkov <bp@alien8.de> Link: http://lkml.kernel.org/r/20130904131602.GC2564@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* sched: Ensure update_cfs_shares() is called for parents of ↵Peter Zijlstra2013-08-20
| | | | | | | | | | | | | | | | | | | | | | | | continuously-running tasks commit bf0bd948d1682e3996adc093b43021ed391983e6 upstream. We typically update a task_group's shares within the dequeue/enqueue path. However, continuously running tasks sharing a CPU are not subject to these updates as they are only put/picked. Unfortunately, when we reverted f269ae046 (in 17bc14b7), we lost the augmenting periodic update that was supposed to account for this; resulting in a potential loss of fairness. To fix this, re-introduce the explicit update in update_cfs_rq_blocked_load() [called via entity_tick()]. Reported-by: Max Hailperin <max@gustavus.edu> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Paul Turner <pjt@google.com> Link: http://lkml.kernel.org/n/tip-9545m3apw5d93ubyrotrj31y@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* Merge branch 'sched-urgent-for-linus' of ↵Linus Torvalds2013-06-20
|\ | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler fixes from Ingo Molnar: "Two smaller fixes - plus a context tracking tracing fix that is a bit bigger" * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: tracing/context-tracking: Add preempt_schedule_context() for tracing sched: Fix clear NOHZ_BALANCE_KICK sched/x86: Construct all sibling maps if smt
| * sched: Fix clear NOHZ_BALANCE_KICKVincent Guittot2013-06-19
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | I have faced a sequence where the Idle Load Balance was sometime not triggered for a while on my platform, in the following scenario: CPU 0 and CPU 1 are running tasks and CPU 2 is idle CPU 1 kicks the Idle Load Balance CPU 1 selects CPU 2 as the new Idle Load Balancer CPU 2 sets NOHZ_BALANCE_KICK for CPU 2 CPU 2 sends a reschedule IPI to CPU 2 While CPU 3 wakes up, CPU 0 or CPU 1 migrates a waking up task A on CPU 2 CPU 2 finally wakes up, runs task A and discards the Idle Load Balance task A quickly goes back to sleep (before a tick occurs on CPU 2) CPU 2 goes back to idle with NOHZ_BALANCE_KICK set Whenever CPU 2 will be selected as the ILB, no reschedule IPI will be sent because NOHZ_BALANCE_KICK is already set and no Idle Load Balance will be performed. We must wait for the sched softirq to be raised on CPU 2 thanks to another part the kernel to come back to clear NOHZ_BALANCE_KICK. The proposed solution clears NOHZ_BALANCE_KICK in schedule_ipi if we can't raise the sched_softirq for the Idle Load Balance. Change since V1: - move the clear of NOHZ_BALANCE_KICK in got_nohz_idle_kick if the ILB can't run on this CPU (as suggested by Peter) Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1370419991-13870-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* | vtime: Use consistent clocks among nohz accountingFrederic Weisbecker2013-05-31
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | While computing the cputime delta of dynticks CPUs, we are mixing up clocks of differents natures: * local_clock() which takes care of unstable clock sources and fix these if needed. * sched_clock() which is the weaker version of local_clock(). It doesn't compute any fixup in case of unstable source. If the clock source is stable, those two clocks are the same and we can safely compute the difference against two random points. Otherwise it results in random deltas as sched_clock() can randomly drift away, back or forward, from local_clock(). As a consequence, some strange behaviour with unstable tsc has been observed such as non progressing constant zero cputime. (The 'top' command showing no load). Fix this by only using local_clock(), or its irq safe/remote equivalent, in vtime code. Reported-by: Mike Galbraith <efault@gmx.de> Suggested-by: Mike Galbraith <efault@gmx.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Merge branch 'timers-nohz-for-linus' of ↵Linus Torvalds2013-05-05
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull 'full dynticks' support from Ingo Molnar: "This tree from Frederic Weisbecker adds a new, (exciting! :-) core kernel feature to the timer and scheduler subsystems: 'full dynticks', or CONFIG_NO_HZ_FULL=y. This feature extends the nohz variable-size timer tick feature from idle to busy CPUs (running at most one task) as well, potentially reducing the number of timer interrupts significantly. This feature got motivated by real-time folks and the -rt tree, but the general utility and motivation of full-dynticks runs wider than that: - HPC workloads get faster: CPUs running a single task should be able to utilize a maximum amount of CPU power. A periodic timer tick at HZ=1000 can cause a constant overhead of up to 1.0%. This feature removes that overhead - and speeds up the system by 0.5%-1.0% on typical distro configs even on modern systems. - Real-time workload latency reduction: CPUs running critical tasks should experience as little jitter as possible. The last remaining source of kernel-related jitter was the periodic timer tick. - A single task executing on a CPU is a pretty common situation, especially with an increasing number of cores/CPUs, so this feature helps desktop and mobile workloads as well. The cost of the feature is mainly related to increased timer reprogramming overhead when a CPU switches its tick period, and thus slightly longer to-idle and from-idle latency. Configuration-wise a third mode of operation is added to the existing two NOHZ kconfig modes: - CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named as a config option. This is the traditional Linux periodic tick design: there's a HZ tick going on all the time, regardless of whether a CPU is idle or not. - CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the periodic tick when a CPU enters idle mode. - CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the tick when a CPU is idle, also slows the tick down to 1 Hz (one timer interrupt per second) when only a single task is running on a CPU. The .config behavior is compatible: existing !CONFIG_NO_HZ and CONFIG_NO_HZ=y settings get translated to the new values, without the user having to configure anything. CONFIG_NO_HZ_FULL is turned off by default. This feature is based on a lot of infrastructure work that has been steadily going upstream in the last 2-3 cycles: related RCU support and non-periodic cputime support in particular is upstream already. This tree adds the final pieces and activates the feature. The pull request is marked RFC because: - it's marked 64-bit only at the moment - the 32-bit support patch is small but did not get ready in time. - it has a number of fresh commits that came in after the merge window. The overwhelming majority of commits are from before the merge window, but still some aspects of the tree are fresh and so I marked it RFC. - it's a pretty wide-reaching feature with lots of effects - and while the components have been in testing for some time, the full combination is still not very widely used. That it's default-off should reduce its regression abilities and obviously there are no known regressions with CONFIG_NO_HZ_FULL=y enabled either. - the feature is not completely idempotent: there is no 100% equivalent replacement for a periodic scheduler/timer tick. In particular there's ongoing work to map out and reduce its effects on scheduler load-balancing and statistics. This should not impact correctness though, there are no known regressions related to this feature at this point. - it's a pretty ambitious feature that with time will likely be enabled by most Linux distros, and we'd like you to make input on its design/implementation, if you dislike some aspect we missed. Without flaming us to crisp! :-) Future plans: - there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off the periodic tick altogether when there's a single busy task on a CPU. We'd first like 1 Hz to be exposed more widely before we go for the 0 Hz target though. - once we reach 0 Hz we can remove the periodic tick assumption from nr_running>=2 as well, by essentially interrupting busy tasks only as frequently as the sched_latency constraints require us to do - once every 4-40 msecs, depending on nr_running. I am personally leaning towards biting the bullet and doing this in v3.10, like the -rt tree this effort has been going on for too long - but the final word is up to you as usual. More technical details can be found in Documentation/timers/NO_HZ.txt" * 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits) sched: Keep at least 1 tick per second for active dynticks tasks rcu: Fix full dynticks' dependency on wide RCU nocb mode nohz: Protect smp_processor_id() in tick_nohz_task_switch() nohz_full: Add documentation. cputime_nsecs: use math64.h for nsec resolution conversion helpers nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config nohz: Reduce overhead under high-freq idling patterns nohz: Remove full dynticks' superfluous dependency on RCU tree nohz: Fix unavailable tick_stop tracepoint in dynticks idle nohz: Add basic tracing nohz: Select wide RCU nocb for full dynticks nohz: Disable the tick when irq resume in full dynticks CPU nohz: Re-evaluate the tick for the new task after a context switch nohz: Prepare to stop the tick on irq exit nohz: Implement full dynticks kick nohz: Re-evaluate the tick from the scheduler IPI sched: New helper to prevent from stopping the tick in full dynticks sched: Kick full dynticks CPU that have more than one task enqueued. perf: New helper to prevent full dynticks CPUs from stopping tick perf: Kick full dynticks CPU if events rotation is needed ...
| * sched: Keep at least 1 tick per second for active dynticks tasksFrederic Weisbecker2013-05-04
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The scheduler doesn't yet fully support environments with a single task running without a periodic tick. In order to ensure we still maintain the duties of scheduler_tick(), keep at least 1 tick per second. This makes sure that we keep the progression of various scheduler accounting and background maintainance even with a very low granularity. Examples include cpu load, sched average, CFS entity vruntime, avenrun and events such as load balancing, amongst other details handled in sched_class::task_tick(). This limitation will be removed in the future once we get these individual items to work in full dynticks CPUs. Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Christoph Lameter <cl@linux.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: 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>
| * Merge commit '8700c95adb03' into timers/nohzFrederic Weisbecker2013-05-02
| |\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
| * | nohz: Re-evaluate the tick for the new task after a context switchFrederic Weisbecker2013-04-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When a task is scheduled in, it may have some properties of its own that could make the CPU reconsider the need for the tick: posix cpu timers, perf events, ... So notify the full dynticks subsystem when a task gets scheduled in and re-check the tick dependency at this stage. This is done through a self IPI to avoid messing up with any current lock scenario. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> 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: Oleg Nesterov <oleg@redhat.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>
| * | nohz: Re-evaluate the tick from the scheduler IPIFrederic Weisbecker2013-04-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The scheduler IPI is used by the scheduler to kick full dynticks CPUs asynchronously when more than one task are running or when a new timer list timer is enqueued. This way the destination CPU can decide to restart the tick to handle this new situation. Now let's call that kick in the scheduler IPI. (Reusing the scheduler IPI rather than implementing a new IPI was suggested by Peter Zijlstra a while ago) Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> 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: Oleg Nesterov <oleg@redhat.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>
| * | sched: New helper to prevent from stopping the tick in full dynticksFrederic Weisbecker2013-04-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Provide a new helper to be called from the full dynticks engine before stopping the tick in order to make sure we don't stop it when there is more than one task running on the CPU. This way we make sure that the tick stays alive to maintain fairness. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> 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: Oleg Nesterov <oleg@redhat.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>
| * | sched: Kick full dynticks CPU that have more than one task enqueued.Frederic Weisbecker2013-04-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Kick the tick on full dynticks CPUs when they get more than one task running on their queue. This makes sure that local fairness is maintained by the tick on the destination. This is done regardless of these tasks' class. We should be able to be more clever in the future depending on these. eg: a CPU that runs a SCHED_FIFO task doesn't need to maintain fairness against local pending tasks of the fair class. But keep things simple for now. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> 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: Oleg Nesterov <oleg@redhat.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>
| * | nohz: Switch from "extended nohz" to "full nohz" based namingFrederic Weisbecker2013-04-15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | "Extended nohz" was used as a naming base for the full dynticks API and Kconfig symbols. It reflects the fact the system tries to stop the tick in more places than just idle. But that "extended" name is a bit opaque and vague. Rename it to "full" makes it clearer what the system tries to do under this config: try to shutdown the tick anytime it can. The various constraints that prevent that to happen shouldn't be considered as fundamental properties of this feature but rather technical issues that may be solved in the future. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> 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: 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>
| * | nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMONFrederic Weisbecker2013-04-03
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
| * | nohz: Wake up full dynticks CPUs when a timer gets enqueuedFrederic Weisbecker2013-03-21
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Wake up a CPU when a timer list timer is enqueued there and the target is part of the full dynticks range. Sending an IPI to it makes it reconsidering the next timer to program on top of recent updates. This may later be improved by checking if the tick is really stopped on the target. This would need some careful synchronization though. So deal with such optimization later and start simple. 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>
* | | Merge branch 'sched-urgent-for-linus' of ↵Linus Torvalds2013-05-02
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler fixes from Ingo Molnar: "This fixes the cputime scaling overflow problems for good without having bad 32-bit overhead, and gets rid of the div64_u64_rem() helper as well." * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: Revert "math64: New div64_u64_rem helper" sched: Avoid prev->stime underflow sched: Do not account bogus utime sched: Avoid cputime scaling overflow
| * | | sched: Avoid prev->stime underflowStanislaw Gruszka2013-04-30
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Dave Hansen reported strange utime/stime values on his system: https://lkml.org/lkml/2013/4/4/435 This happens because prev->stime value is bigger than rtime value. Root of the problem are non-monotonic rtime values (i.e. current rtime is smaller than previous rtime) and that should be debugged and fixed. But since problem did not manifest itself before commit 62188451f0d63add7ad0cd2a1ae269d600c1663d "cputime: Avoid multiplication overflow on utime scaling", it should be threated as regression, which we can easily fixed on cputime_adjust() function. For now, let's apply this fix, but further work is needed to fix root of the problem. Reported-and-tested-by: Dave Hansen <dave@sr71.net> Cc: <stable@vger.kernel.org> # 3.9+ Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1367314507-9728-3-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
| * | | sched: Do not account bogus utimeStanislaw Gruszka2013-04-30
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Due to rounding in scale_stime(), for big numbers, scaled stime values will grow in chunks. Since rtime grow in jiffies and we calculate utime like below: prev->stime = max(prev->stime, stime); prev->utime = max(prev->utime, rtime - prev->stime); we could erroneously account stime values as utime. To prevent that only update prev->{u,s}time values when they are smaller than current rtime. Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
| * | | sched: Avoid cputime scaling overflowStanislaw Gruszka2013-04-30
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Here is patch, which adds Linus's cputime scaling algorithm to the kernel. This is a follow up (well, fix) to commit d9a3c9823a2e6a543eb7807fb3d15d8233817ec5 ("sched: Lower chances of cputime scaling overflow") which commit tried to avoid multiplication overflow, but did not guarantee that the overflow would not happen. Linus crated a different algorithm, which completely avoids the multiplication overflow by dropping precision when numbers are big. It was tested by me and it gives good relative error of scaled numbers. Testing method is described here: http://marc.info/?l=linux-kernel&m=136733059505406&w=2 Originally-From: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20130430151441.GC10465@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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