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2011-03-04sched: Fix sched rt group scheduling when hierachy is enabledBalbir Singh
The current sched rt code is broken when it comes to hierarchical scheduling, this patch fixes two problems 1. It adds redundant enqueuing (harmless) when it finds a queue has tasks enqueued, but it has no run time and it is not throttled. 2. The most important change is in sched_rt_rq_enqueue/dequeue. The code just picks the rt_rq belonging to the current cpu on which the period timer runs, the patch fixes it, so that the correct rt_se is enqueued/dequeued. Tested with a simple hierarchy /c/d, c and d assigned similar runtimes of 50,000 and a while 1 loop runs within "d". Both c and d get throttled, without the patch, the task just stops running and never runs (depends on where the sched_rt b/w timer runs). With the patch, the task is throttled and runs as expected. [ bharata, suggestions on how to pick the rt_se belong to the rt_rq and correct cpu ] Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com> Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: stable@kernel.org LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-03sched: Fix update_curr_rt()Peter Zijlstra
cpu_stopper_thread() migration_cpu_stop() __migrate_task() deactivate_task() dequeue_task() dequeue_task_rq() update_curr_rt() Will call update_curr_rt() on rq->curr, which at that time is rq->stop. The problem is that rq->stop.prio matches an RT prio and thus falsely assumes its a rt_sched_class task. Reported-Debuged-Tested-Acked-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Cc: stable@kernel.org # .37 Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18sched: Implement on-demand (active) cfs_rq listPeter Zijlstra
Make certain load-balance actions scale per number of active cgroups instead of the number of existing cgroups. This makes wakeup/sleep paths more expensive, but is a win for systems where the vast majority of existing cgroups are idle. Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20101115234937.666535048@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-10-18sched: Do not account irq time to current taskVenkatesh Pallipadi
Scheduler accounts both softirq and interrupt processing times to the currently running task. This means, if the interrupt processing was for some other task in the system, then the current task ends up being penalized as it gets shorter runtime than otherwise. Change sched task accounting to acoount only actual task time from currently running task. Now update_curr(), modifies the delta_exec to depend on rq->clock_task. Note that this change only handles CONFIG_IRQ_TIME_ACCOUNTING case. We can extend this to CONFIG_VIRT_CPU_ACCOUNTING with minimal effort. But, thats for later. This change will impact scheduling behavior in interrupt heavy conditions. Tested on a 4-way system with eth0 handled by CPU 2 and a network heavy task (nc) running on CPU 3 (and no RSS/RFS). With that I have CPU 2 spending 75%+ of its time in irq processing. CPU 3 spending around 35% time running nc task. Now, if I run another CPU intensive task on CPU 2, without this change /proc/<pid>/schedstat shows 100% of time accounted to this task. With this change, it rightly shows less than 25% accounted to this task as remaining time is actually spent on irq processing. Signed-off-by: Venkatesh Pallipadi <venki@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1286237003-12406-7-git-send-email-venki@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-10-18sched: Unindent labelsPeter Zijlstra
Labels should be on column 0. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-09-21sched: Give CPU bound RT tasks preferenceSteven Rostedt
If a high priority task is waking up on a CPU that is running a lower priority task that is bound to a CPU, see if we can move the high RT task to another CPU first. Note, if all other CPUs are running higher priority tasks than the CPU bounded current task, then it will be preempted regardless. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Gregory Haskins <ghaskins@novell.com> LKML-Reference: <20100921024138.888922071@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-09-21sched: Try not to migrate higher priority RT tasksSteven Rostedt
When first working on the RT scheduler design, we concentrated on keeping all CPUs running RT tasks instead of having multiple RT tasks on a single CPU waiting for the migration thread to move them. Instead we take a more proactive stance and push or pull RT tasks from one CPU to another on wakeup or scheduling. When an RT task wakes up on a CPU that is running another RT task, instead of preempting it and killing the cache of the running RT task, we look to see if we can migrate the RT task that is waking up, even if the RT task waking up is of higher priority. This may sound a bit odd, but RT tasks should be limited in migration by the user anyway. But in practice, people do not do this, which causes high prio RT tasks to bounce around the CPUs. This becomes even worse when we have priority inheritance, because a high prio task can block on a lower prio task and boost its priority. When the lower prio task wakes up the high prio task, if it happens to be on the same CPU it will migrate off of it. But in reality, the above does not happen much either, because the wake up of the lower prio task, which has already been boosted, if it was on the same CPU as the higher prio task, it would then migrate off of it. But anyway, we do not want to migrate them either. To examine the scheduling, I created a test program and examined it under kernelshark. The test program created CPU * 2 threads, where each thread had a different priority. The program takes different options. The options used in this change log was to have priority inheritance mutexes or not. All threads did the following loop: static void grab_lock(long id, int iter, int l) { ftrace_write("thread %ld iter %d, taking lock %d\n", id, iter, l); pthread_mutex_lock(&locks[l]); ftrace_write("thread %ld iter %d, took lock %d\n", id, iter, l); busy_loop(nr_tasks - id); ftrace_write("thread %ld iter %d, unlock lock %d\n", id, iter, l); pthread_mutex_unlock(&locks[l]); } void *start_task(void *id) { [...] while (!done) { for (l = 0; l < nr_locks; l++) { grab_lock(id, i, l); ftrace_write("thread %ld iter %d sleeping\n", id, i); ms_sleep(id); } i++; } [...] } The busy_loop(ms) keeps the CPU spinning for ms milliseconds. The ms_sleep(ms) sleeps for ms milliseconds. The ftrace_write() writes to the ftrace buffer to help analyze via ftrace. The higher the id, the higher the prio, the shorter it does the busy loop, but the longer it spins. This is usually the case with RT tasks, the lower priority tasks usually run longer than higher priority tasks. At the end of the test, it records the number of loops each thread took, as well as the number of voluntary preemptions, non-voluntary preemptions, and number of migrations each thread took, taking the information from /proc/$$/sched and /proc/$$/status. Running this on a 4 CPU processor, the results without changes to the kernel looked like this: Task vol nonvol migrated iterations ---- --- ------ -------- ---------- 0: 53 3220 1470 98 1: 562 773 724 98 2: 752 933 1375 98 3: 749 39 697 98 4: 758 5 515 98 5: 764 2 679 99 6: 761 2 535 99 7: 757 3 346 99 total: 5156 4977 6341 787 Each thread regardless of priority migrated a few hundred times. The higher priority tasks, were a little better but still took quite an impact. By letting higher priority tasks bump the lower prio task from the CPU, things changed a bit: Task vol nonvol migrated iterations ---- --- ------ -------- ---------- 0: 37 2835 1937 98 1: 666 1821 1865 98 2: 654 1003 1385 98 3: 664 635 973 99 4: 698 197 352 99 5: 703 101 159 99 6: 708 1 75 99 7: 713 1 2 99 total: 4843 6594 6748 789 The total # of migrations did not change (several runs showed the difference all within the noise). But we now see a dramatic improvement to the higher priority tasks. (kernelshark showed that the watchdog timer bumped the highest priority task to give it the 2 count. This was actually consistent with every run). Notice that the # of iterations did not change either. The above was with priority inheritance mutexes. That is, when the higher prority task blocked on a lower priority task, the lower priority task would inherit the higher priority task (which shows why task 6 was bumped so many times). When not using priority inheritance mutexes, the current kernel shows this: Task vol nonvol migrated iterations ---- --- ------ -------- ---------- 0: 56 3101 1892 95 1: 594 713 937 95 2: 625 188 618 95 3: 628 4 491 96 4: 640 7 468 96 5: 631 2 501 96 6: 641 1 466 96 7: 643 2 497 96 total: 4458 4018 5870 765 Not much changed with or without priority inheritance mutexes. But if we let the high priority task bump lower priority tasks on wakeup we see: Task vol nonvol migrated iterations ---- --- ------ -------- ---------- 0: 115 3439 2782 98 1: 633 1354 1583 99 2: 652 919 1218 99 3: 645 713 934 99 4: 690 3 3 99 5: 694 1 4 99 6: 720 3 4 99 7: 747 0 1 100 Which shows a even bigger change. The big difference between task 3 and task 4 is because we have only 4 CPUs on the machine, causing the 4 highest prio tasks to always have preference. Although I did not measure cache misses, and I'm sure there would be little to measure since the test was not data intensive, I could imagine large improvements for higher priority tasks when dealing with lower priority tasks. Thus, I'm satisfied with making the change and agreeing with what Gregory Haskins argued a few years ago when we first had this discussion. One final note. All tasks in the above tests were RT tasks. Any RT task will always preempt a non RT task that is running on the CPU the RT task wants to run on. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Gregory Haskins <ghaskins@novell.com> LKML-Reference: <20100921024138.605460343@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-06-18sched: task_tick_rt: Remove the obsolete ->signal != NULL checkOleg Nesterov
Remove the obsolete ->signal != NULL check in watchdog(). Since ea6d290c ->signal can't be NULL. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100610230948.GA25911@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-04-02sched: Add enqueue/dequeue flagsPeter Zijlstra
In order to reduce the dependency on TASK_WAKING rework the enqueue interface to support a proper flags field. Replace the int wakeup, bool head arguments with an int flags argument and create the following flags: ENQUEUE_WAKEUP - the enqueue is a wakeup of a sleeping task, ENQUEUE_WAKING - the enqueue has relative vruntime due to having sched_class::task_waking() called, ENQUEUE_HEAD - the waking task should be places on the head of the priority queue (where appropriate). For symmetry also convert sched_class::dequeue() to a flags scheme. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-04-02sched: Fix TASK_WAKING vs fork deadlockPeter Zijlstra
Oleg noticed a few races with the TASK_WAKING usage on fork. - since TASK_WAKING is basically a spinlock, it should be IRQ safe - since we set TASK_WAKING (*) without holding rq->lock it could be there still is a rq->lock holder, thereby not actually providing full serialization. (*) in fact we clear PF_STARTING, which in effect enables TASK_WAKING. Cure the second issue by not setting TASK_WAKING in sched_fork(), but only temporarily in wake_up_new_task() while calling select_task_rq(). Cure the first by holding rq->lock around the select_task_rq() call, this will disable IRQs, this however requires that we push down the rq->lock release into select_task_rq_fair()'s cgroup stuff. Because select_task_rq_fair() still needs to drop the rq->lock we cannot fully get rid of TASK_WAKING. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-04-02Merge branch 'linus' into sched/coreIngo Molnar
Merge reason: update to latest upstream Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-03-13Merge branch 'sched-fixes-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: sched: Fix pick_next_highest_task_rt() for cgroups sched: Cleanup: remove unused variable in try_to_wake_up() x86: Fix sched_clock_cpu for systems with unsynchronized TSC
2010-03-11sched: Implement group scheduler statistics in one structLucas De Marchi
Put all statistic fields of sched_entity in one struct, sched_statistics, and embed it into sched_entity. This change allows to memset the sched_statistics to 0 when needed (for instance when forking), avoiding bugs of non initialized fields. Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1268275065-18542-1-git-send-email-lucas.de.marchi@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-03-11sched: Fix pick_next_highest_task_rt() for cgroupsPeter Zijlstra
Since pick_next_highest_task_rt() already iterates all the cgroups and is really only interested in tasks, skip over the !task entries. Reported-by: Dhaval Giani <dhaval.giani@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Tested-by: Dhaval Giani <dhaval.giani@gmail.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-03-06kernel core: use helpers for rlimitsJiri Slaby
Make sure compiler won't do weird things with limits. E.g. fetching them twice may return 2 different values after writable limits are implemented. I.e. either use rlimit helpers added in commit 3e10e716abf3 ("resource: add helpers for fetching rlimits") or ACCESS_ONCE if not applicable. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: john stultz <johnstul@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-02-04sched: Change usage of rt_rq->rt_se to rt_rq->tg->rt_se[cpu]Yong Zhang
This is the first step to remove rt_rq member rt_se because it have the same meaning with tg->rt_se[cpu]. And the latter style is also used by the fair scheduling class. Signed-off-by: Yong Zhang <yong.zhang0@gmail.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <2674af741001282257r28c97a92o9f90cf16fe8d3d84@mail.gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-01-22sched: Implement head queueing for sched_rtThomas Gleixner
The ability of enqueueing a task to the head of a SCHED_FIFO priority list is required to fix some violations of POSIX scheduling policy. Implement the functionality in sched_rt. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Carsten Emde <cbe@osadl.org> Tested-by: Mathias Weber <mathias.weber.mw1@roche.com> LKML-Reference: <20100120171629.772169931@linutronix.de>
2010-01-22sched: Extend enqueue_task to allow head queueingThomas Gleixner
The ability of enqueueing a task to the head of a SCHED_FIFO priority list is required to fix some violations of POSIX scheduling policy. Extend the related functions with a "head" argument. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Carsten Emde <cbe@osadl.org> Tested-by: Mathias Weber <mathias.weber.mw1@roche.com> LKML-Reference: <20100120171629.734886007@linutronix.de>
2010-01-21sched: Remove the sched_class load_balance methodsPeter Zijlstra
Take out the sched_class methods for load-balancing. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-01-17sched: Don't expose local functionsH Hartley Sweeten
kernel/sched: don't expose local functions The get_rr_interval_* functions are all class methods of struct sched_class. They are not exported so make them static. Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com> Cc: Peter Zijlstra <peterz@infradead.org> LKML-Reference: <201001132021.53253.hartleys@visionengravers.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-12-16sched: Add pre and post wakeup hooksPeter Zijlstra
As will be apparent in the next patch, we need a pre wakeup hook for sched_fair task migration, hence rename the post wakeup hook and one pre wakeup. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> LKML-Reference: <20091216170518.114746117@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-12-14sched: Convert rt_runtime_lock to raw_spinlockThomas Gleixner
Convert locks which cannot be sleeping locks in preempt-rt to raw_spinlocks. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Ingo Molnar <mingo@elte.hu>
2009-12-14sched: Convert rq->lock to raw_spinlockThomas Gleixner
Convert locks which cannot be sleeping locks in preempt-rt to raw_spinlocks. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Ingo Molnar <mingo@elte.hu>
2009-12-09sched: Protect sched_rr_get_param() access to task->sched_classThomas Gleixner
sched_rr_get_param calls task->sched_class->get_rr_interval(task) without protection against a concurrent sched_setscheduler() call which modifies task->sched_class. Serialize the access with task_rq_lock(task) and hand the rq pointer into get_rr_interval() as it's needed at least in the sched_fair implementation. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> LKML-Reference: <alpine.LFD.2.00.0912090930120.3089@localhost.localdomain> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-11-04cpumask: Simplify sched_rt.cRusty Russell
find_lowest_rq() wants to call pick_optimal_cpu() on the intersection of sched_domain_span(sd) and lowest_mask. Rather than doing a cpus_and into a temporary, we can open-code it. This actually makes the code slightly clearer, IMHO. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Acked-by: Gregory Haskins <ghaskins@novell.com> Cc: Steven Rostedt <rostedt@goodmis.org> LKML-Reference: <200911031453.15350.rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-21sched: Simplify sys_sched_rr_get_interval() system callPeter Williams
By removing the need for it to know details of scheduling classes. This allows PlugSched to define orthogonal scheduling classes. Signed-off-by: Peter Williams <pwil3058@bigpond.net.au> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> LKML-Reference: <06d1b89ee15a0eef82d7.1253496713@mudlark.pw.nest> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-15sched: Rename sync argumentsPeter Zijlstra
In order to extend the functions to have more than 1 flag (sync), rename the argument to flags, and explicitly define a WF_ space for individual flags. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-15sched: Rename select_task_rq() argumentPeter Zijlstra
In order to be able to rename the sync argument, we need to rename the current flag argument. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-15sched: Hook sched_balance_self() into sched_class::select_task_rq()Peter Zijlstra
Rather ugly patch to fully place the sched_balance_self() code inside the fair class. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-04sched: Scale down cpu_power due to RT tasksPeter Zijlstra
Keep an average on the amount of time spend on RT tasks and use that fraction to scale down the cpu_power for regular tasks. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Tested-by: Andreas Herrmann <andreas.herrmann3@amd.com> Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com> Acked-by: Gautham R Shenoy <ego@in.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> LKML-Reference: <20090901083826.287778431@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Fix cpupri build on !CONFIG_SMPIngo Molnar
This build bug: In file included from kernel/sched.c:1765: kernel/sched_rt.c: In function ‘has_pushable_tasks’: kernel/sched_rt.c:1069: error: ‘struct rt_rq’ has no member named ‘pushable_tasks’ kernel/sched_rt.c: In function ‘pick_next_task_rt’: kernel/sched_rt.c:1084: error: ‘struct rq’ has no member named ‘post_schedule’ Triggers because both pushable_tasks and post_schedule are SMP-only fields. Move pushable_tasks() to the SMP section and #ifdef the post_schedule use. Cc: Gregory Haskins <ghaskins@novell.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090729150422.17691.55590.stgit@dev.haskins.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Add debug check to task_of()Peter Zijlstra
A frequent mistake appears to be to call task_of() on a scheduler entity that is not actually a task, which can result in a wild pointer. Add a check to catch these mistakes. Suggested-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Fully integrate cpus_active_map and root-domain codeGregory Haskins
Reflect "active" cpus in the rq->rd->online field, instead of the online_map. The motivation is that things that use the root-domain code (such as cpupri) only care about cpus classified as "active" anyway. By synchronizing the root-domain state with the active map, we allow several optimizations. For instance, we can remove an extra cpumask_and from the scheduler hotpath by utilizing rq->rd->online (since it is now a cached version of cpu_active_map & rq->rd->span). Signed-off-by: Gregory Haskins <ghaskins@novell.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Max Krasnyansky <maxk@qualcomm.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090730145723.25226.24493.stgit@dev.haskins.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-02sched: Enhance the pre/post scheduling logicGregory Haskins
We currently have an explicit "needs_post" vtable method which returns a stack variable for whether we should later run post-schedule. This leads to an awkward exchange of the variable as it bubbles back up out of the context switch. Peter Zijlstra observed that this information could be stored in the run-queue itself instead of handled on the stack. Therefore, we revert to the method of having context_switch return void, and update an internal rq->post_schedule variable when we require further processing. In addition, we fix a race condition where we try to access current->sched_class without holding the rq->lock. This is technically racy, as the sched-class could change out from under us. Instead, we reference the per-rq post_schedule variable with the runqueue unlocked, but with preemption disabled to see if we need to reacquire the rq->lock. Finally, we clean the code up slightly by removing the #ifdef CONFIG_SMP conditionals from the schedule() call, and implement some inline helper functions instead. This patch passes checkpatch, and rt-migrate. Signed-off-by: Gregory Haskins <ghaskins@novell.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090729150422.17691.55590.stgit@dev.haskins.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-07-10sched_rt: Fix overload bug on rt group schedulingPeter Zijlstra
Fixes an easily triggerable BUG() when setting process affinities. Make sure to count the number of migratable tasks in the same place: the root rt_rq. Otherwise the number doesn't make sense and we'll hit the BUG in set_cpus_allowed_rt(). Also, make sure we only count tasks, not groups (this is probably already taken care of by the fact that rt_se->nr_cpus_allowed will be 0 for groups, but be more explicit) Tested-by: Thomas Gleixner <tglx@linutronix.de> CC: stable@kernel.org Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Gregory Haskins <ghaskins@novell.com> LKML-Reference: <1247067476.9777.57.camel@twins> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-06-09cpumask: alloc zeroed cpumask for static cpumask_var_tsYinghai Lu
These are defined as static cpumask_var_t so if MAXSMP is not used, they are cleared already. Avoid surprises when MAXSMP is enabled. Signed-off-by: Yinghai Lu <yinghai.lu@kernel.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2009-04-08Merge commit 'v2.6.30-rc1' into sched/urgentIngo Molnar
Merge reason: update to latest upstream to queue up fix Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-04-01sched_rt: don't allocate cpumask in fastpathRusty Russell
Impact: cleanup As pointed out by Steven Rostedt. Since the arg in question is unused, we simply change cpupri_find() to accept NULL. Reported-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> LKML-Reference: <200903251501.22664.rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-03-27Merge branch 'core/percpu' into percpu-cpumask-x86-for-linus-2Ingo Molnar
Conflicts: arch/parisc/kernel/irq.c arch/x86/include/asm/fixmap_64.h arch/x86/include/asm/setup.h kernel/irq/handle.c Semantic merge: arch/x86/include/asm/fixmap.h Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-08Merge branches 'sched/rt' and 'sched/urgent' into sched/coreIngo Molnar
2009-02-01sched_rt: don't use first_cpu on cpumask created with cpumask_andRusty Russell
cpumask_and() only initializes nr_cpu_ids bits, so the (deprecated) first_cpu() might find one of those uninitialized bits if nr_cpu_ids is less than NR_CPUS (as it can be for CONFIG_CPUMASK_OFFSTACK). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-16sched: make plist a library facilityPeter Zijlstra
Ingo Molnar wrote: > here's a new build failure with tip/sched/rt: > > LD .tmp_vmlinux1 > kernel/built-in.o: In function `set_curr_task_rt': > sched.c:(.text+0x3675): undefined reference to `plist_del' > kernel/built-in.o: In function `pick_next_task_rt': > sched.c:(.text+0x37ce): undefined reference to `plist_del' > kernel/built-in.o: In function `enqueue_pushable_task': > sched.c:(.text+0x381c): undefined reference to `plist_del' Eliminate the plist library kconfig and make it available unconditionally. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-14sched: fix build error in kernel/sched_rt.c when RT_GROUP_SCHED && !SMPGregory Haskins
Ingo found a build error in the scheduler when RT_GROUP_SCHED was enabled, but SMP was not. This patch rearranges the code such that it is a little more streamlined and compiles under all permutations of SMP, UP and RT_GROUP_SCHED. It was boot tested on my 4-way x86_64 and it still passes preempt-test. Signed-off-by: Gregory Haskins <ghaskins@novell.com>
2009-01-14sched: de CPP-ify the scheduler codeGregory Haskins
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
2009-01-11cpumask: reduce stack usage in find_lowest_rqMike Travis
Impact: reduce stack usage, cleanup Use a cpumask_var_t in find_lowest_rq() and clean up other old cpumask_t calls. Signed-off-by: Mike Travis <travis@sgi.com>
2009-01-11Merge branch 'sched/latest' of ↵Ingo Molnar
git://git.kernel.org/pub/scm/linux/kernel/git/ghaskins/linux-2.6-hacks into sched/rt
2009-01-03sched: put back some stack hog changes that were undone in kernel/sched.cMike Travis
Impact: prevents panic from stack overflow on numa-capable machines. Some of the "removal of stack hogs" changes in kernel/sched.c by using node_to_cpumask_ptr were undone by the early cpumask API updates, and causes a panic due to stack overflow. This patch undoes those changes by using cpumask_of_node() which returns a 'const struct cpumask *'. In addition, cpu_coregoup_map is replaced with cpu_coregroup_mask further reducing stack usage. (Both of these updates removed 9 FIXME's!) Also: Pick up some remaining changes from the old 'cpumask_t' functions to the new 'struct cpumask *' functions. Optimize memory traffic by allocating each percpu local_cpu_mask on the same node as the referring cpu. Signed-off-by: Mike Travis <travis@sgi.com> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-03Merge branch 'master' of ↵Mike Travis
git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-cpumask into merge-rr-cpumask Conflicts: arch/x86/kernel/io_apic.c kernel/rcuclassic.c kernel/sched.c kernel/time/tick-sched.c Signed-off-by: Mike Travis <travis@sgi.com> [ mingo@elte.hu: backmerged typo fix for io_apic.c ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-12-29RT: fix push_rt_task() to handle dequeue_pushable properlyGregory Haskins
A panic was discovered by Chirag Jog where a BUG_ON sanity check in the new "pushable_task" logic would trigger a panic under certain circumstances: http://lkml.org/lkml/2008/9/25/189 Gilles Carry discovered that the root cause was attributed to the pushable_tasks list getting corrupted in the push_rt_task logic. This was the result of a dropped rq lock in double_lock_balance allowing a task in the process of being pushed to potentially migrate away, and thus corrupt the pushable_tasks() list. I traced back the problem as introduced by the pushable_tasks patch that went in recently. There is a "retry" path in push_rt_task() that actually had a compound conditional to decide whether to retry or exit. I missed the meaning behind the rationale for the virtual "if(!task) goto out;" portion of the compound statement and thus did not handle it properly. The new pushable_tasks logic actually creates three distinct conditions: 1) an untouched and unpushable task should be dequeued 2) a migrated task where more pushable tasks remain should be retried 3) a migrated task where no more pushable tasks exist should exit The original logic mushed (1) and (3) together, resulting in the system dequeuing a migrated task (against an unlocked foreign run-queue nonetheless). To fix this, we get rid of the notion of "paranoid" and we support the three unique conditions properly. The paranoid feature is no longer relevant with the new pushable logic (since pushable naturally limits the loop) anyway, so lets just remove it. Reported-By: Chirag Jog <chirag@linux.vnet.ibm.com> Found-by: Gilles Carry <gilles.carry@bull.net> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
2008-12-29sched: create "pushable_tasks" list to limit pushing to one attemptGregory Haskins
The RT scheduler employs a "push/pull" design to actively balance tasks within the system (on a per disjoint cpuset basis). When a task is awoken, it is immediately determined if there are any lower priority cpus which should be preempted. This is opposed to the way normal SCHED_OTHER tasks behave, which will wait for a periodic rebalancing operation to occur before spreading out load. When a particular RQ has more than 1 active RT task, it is said to be in an "overloaded" state. Once this occurs, the system enters the active balancing mode, where it will try to push the task away, or persuade a different cpu to pull it over. The system will stay in this state until the system falls back below the <= 1 queued RT task per RQ. However, the current implementation suffers from a limitation in the push logic. Once overloaded, all tasks (other than current) on the RQ are analyzed on every push operation, even if it was previously unpushable (due to affinity, etc). Whats more, the operation stops at the first task that is unpushable and will not look at items lower in the queue. This causes two problems: 1) We can have the same tasks analyzed over and over again during each push, which extends out the fast path in the scheduler for no gain. Consider a RQ that has dozens of tasks that are bound to a core. Each one of those tasks will be encountered and skipped for each push operation while they are queued. 2) There may be lower-priority tasks under the unpushable task that could have been successfully pushed, but will never be considered until either the unpushable task is cleared, or a pull operation succeeds. The net result is a potential latency source for mid priority tasks. This patch aims to rectify these two conditions by introducing a new priority sorted list: "pushable_tasks". A task is added to the list each time a task is activated or preempted. It is removed from the list any time it is deactivated, made current, or fails to push. This works because a task only needs to be attempted to push once. After an initial failure to push, the other cpus will eventually try to pull the task when the conditions are proper. This also solves the problem that we don't completely analyze all tasks due to encountering an unpushable tasks. Now every task will have a push attempted (when appropriate). This reduces latency both by shorting the critical section of the rq->lock for certain workloads, and by making sure the algorithm considers all eligible tasks in the system. [ rostedt: added a couple more BUG_ONs ] Signed-off-by: Gregory Haskins <ghaskins@novell.com> Acked-by: Steven Rostedt <srostedt@redhat.com>