- 17 Aug, 2024 17 commits
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Peter Zijlstra authored
Extend / fix 86bfbb7c ("sched/fair: Add lag based placement") by noting that lag is fundamentally a temporal measure. It should not be carried around indefinitely. OTOH it should also not be instantly discarded, doing so will allow a task to game the system by purposefully (micro) sleeping at the end of its time quantum. Since lag is intimately tied to the virtual time base, a wall-time based decay is also insufficient, notably competition is required for any of this to make sense. Instead, delay the dequeue and keep the 'tasks' on the runqueue, competing until they are eligible. Strictly speaking, we only care about keeping them until the 0-lag point, but that is a difficult proposition, instead carry them around until they get picked again, and dequeue them at that point. Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by:
Valentin Schneider <vschneid@redhat.com> Tested-by:
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Peter Zijlstra authored
Since special task states must not suffer spurious wakeups, and the proposed delayed dequeue can cause exactly these (under some boundary conditions), propagate this knowledge into dequeue_task() such that it can do the right thing. Signed-off-by:
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Peter Zijlstra authored
The special task states are those that do not suffer spurious wakeups, TASK_FROZEN is very much one of those, mark it as such. Signed-off-by:
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Peter Zijlstra authored
Doing a wakeup on a delayed dequeue task is about as simple as it sounds -- remove the delayed mark and enjoy the fact it was actually still on the runqueue. Signed-off-by:
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Peter Zijlstra authored
Delayed dequeue's natural end is when it gets picked again. Ensure pick_next_task() knows what to do with delayed tasks. Note, this relies on the earlier patch that made pick_next_task() state invariant -- it will restart the pick on dequeue, because obviously the just dequeued task is no longer eligible. Signed-off-by:
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Peter Zijlstra authored
When dequeue_task() is delayed it becomes possible to exit a task (or cgroup) that is still enqueued. Ensure things are dequeued before freeing. Thanks to Valentin for asking the obvious questions and making switched_from_fair() less weird. Signed-off-by:
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Peter Zijlstra authored
Just a little sanity test.. Signed-off-by:
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Peter Zijlstra authored
Delayed dequeue has tasks sit around on the runqueue that are not actually runnable -- specifically, they will be dequeued the moment they get picked. One side-effect is that such a task can get migrated, which leads to a 'nested' dequeue_task() scenario that messes up uclamp if we don't take care. Notably, dequeue_task(DEQUEUE_SLEEP) can 'fail' and keep the task on the runqueue. This however will have removed the task from uclamp -- per uclamp_rq_dec() in dequeue_task(). So far so good. However, if at that point the task gets migrated -- or nice adjusted or any of a myriad of operations that does a dequeue-enqueue cycle -- we'll pass through dequeue_task()/enqueue_task() again. Without modification this will lead to a double decrement for uclamp, which is wrong. Reported-by:
Luis Machado <luis.machado@arm.com> Reported-by:
Hongyan Xia <hongyan.xia2@arm.com> Signed-off-by:
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Peter Zijlstra authored
While most of the delayed dequeue code can be done inside the sched_class itself, there is one location where we do not have an appropriate hook, namely ttwu_runnable(). Add an ENQUEUE_DELAYED call to the on_rq path to deal with waking delayed dequeue tasks. Signed-off-by:
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Peter Zijlstra authored
As a preparation for dequeue_task() failing, and a second code-path needing to take care of the 'success' path, split out the DEQEUE_SLEEP path from deactivate_task(). Much thanks to Libo for spotting and fixing a TASK_ON_RQ_MIGRATING ordering fail. Fixed-by:
Libo Chen <libo.chen@oracle.com> Signed-off-by:
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Peter Zijlstra authored
Working towards delaying dequeue, notably also inside the hierachy, rework dequeue_task_fair() such that it can 'resume' an interrupted hierarchy walk. Signed-off-by:
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Peter Zijlstra authored
Change the function signature of sched_class::dequeue_task() to return a boolean, allowing future patches to 'fail' dequeue. Signed-off-by:
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Peter Zijlstra authored
Implement pick_next_task_fair() in terms of pick_task_fair() to de-duplicate the pick loop. More importantly, this makes all the pick loops use the state-invariant form, which is useful to introduce further re-try conditions in later patches. Signed-off-by:
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Peter Zijlstra authored
With 4c456c9a ("sched/fair: Remove unused 'curr' argument from pick_next_entity()") curr is no longer being used, so no point in clearing it. Signed-off-by:
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Peter Zijlstra authored
Per 54d27365 ("sched/fair: Prevent throttling in early pick_next_task_fair()") the reason check_cfs_rq_runtime() is under the 'if (curr)' check is to ensure the (downward) traversal does not result in an empty cfs_rq. But then the pick_task_fair() 'copy' of all this made it restart the traversal anyway, so that seems to solve the issue too. Signed-off-by:
Ben Segall <bsegall@google.com> Reviewed-by:
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Peter Zijlstra authored
Since commit e8f331bc ("sched/smp: Use lag to simplify cross-runqueue placement") the min_vruntime_copy is no longer used. Signed-off-by:
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Peter Zijlstra authored
Signed-off-by:
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- 07 Aug, 2024 5 commits
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Qais Yousef authored
Some find the name realtime overloaded. Use rt_or_dl() as an alternative, hopefully better, name. Suggested-by:
Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by:
Qais Yousef <qyousef@layalina.io> Signed-off-by:
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Qais Yousef authored
{rt, realtime, dl}_{task, prio}() functions' return value is actually a bool. Convert their return type to reflect that. Suggested-by:"Steven Rostedt (Google)" <rostedt@goodmis.org> Signed-off-by:
Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by:
Metin Kaya <metin.kaya@arm.com> Link: https://lore.kernel.org/r/20240610192018.1567075-3-qyousef@layalina.io
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Qais Yousef authored
rt_task() checks if a task has RT priority. But depends on your dictionary, this could mean it belongs to RT class, or is a 'realtime' task, which includes RT and DL classes. Since this has caused some confusion already on discussion [1], it seemed a clean up is due. I define the usage of rt_task() to be tasks that belong to RT class. Make sure that it returns true only for RT class and audit the users and replace the ones required the old behavior with the new realtime_task() which returns true for RT and DL classes. Introduce similar realtime_prio() to create similar distinction to rt_prio() and update the users that required the old behavior to use the new function. Move MAX_DL_PRIO to prio.h so it can be used in the new definitions. Document the functions to make it more obvious what is the difference between them. PI-boosted tasks is a factor that must be taken into account when choosing which function to use. Rename task_is_realtime() to realtime_task_policy() as the old name is confusing against the new realtime_task(). No functional changes were intended. [1] https://lore.kernel.org/lkml/20240506100509.GL40213@noisy.programming.kicks-ass.net/Signed-off-by:
Phil Auld <pauld@redhat.com> Reviewed-by:
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Dan Carpenter authored
This code has an integer overflow or sign extension bug which was caught by gcc-13: kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow] 341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */ The result is that "fair_server_period_max" is set to 0xfffffffffa000000 (585 years) instead of instead of 0xfa000000 (4 seconds) that was intended. Fix this by changing the type to shift from (1 << 22) to (1UL << 22). Closes: https://lore.kernel.org/all/CA+G9fYtE2GAbeqU+AOCffgo2oH0RTJUxU+=Pi3cFn4di_KgBAQ@mail.gmail.com/ Fixes: d741f297 ("sched/fair: Fair server interface") Reported-by:Linux Kernel Functional Testing <lkft@linaro.org> Reported-by:
Arnd Bergmann <arnd@kernel.org> Reported-by:
Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by:
Dan Carpenter <dan.carpenter@linaro.org> Signed-off-by:
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Tejun Heo authored
balance_fair() skips newidle balancing if rq->nr_running - there are already tasks on the rq, so no need to try to pull tasks. This tests the total number of queued tasks on the CPU instead of only the fair class, but is still correct as the rq can currently only have fair class tasks while balance_fair() is running. However, with the addition of sched_ext below the fair class, this will not hold anymore and make put_prev_task_balance() skip sched_ext's balance() incorrectly as, when a CPU has only lower priority class tasks, rq->nr_running would still be positive and balance_fair() would return 1 even when fair doesn't have any tasks to run. Update balance_fair() to use sched_fair_runnable() which tests rq->cfs.nr_running which is updated by bandwidth throttling. Note that pick_next_task_fair() already uses sched_fair_runnable() in its optimized path for the same purpose. Reported-by:
Tejun Heo <tj@kernel.org> Signed-off-by:
Chengming Zhou <chengming.zhou@linux.dev> Reviewed-by:
K Prateek Nayak <kprateek.nayak@amd.com> Link: https://lore.kernel.org/r/ZrFUjlCf7x3TNXB8@slm.duckdns.org
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- 29 Jul, 2024 18 commits
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Peter Zijlstra authored
The throttle interaction made my brain hurt, make it consistently about 0 transitions of h_nr_running. Signed-off-by: -
Peter Zijlstra authored
Now that fair_server exists, we no longer need RT bandwidth control unless RT_GROUP_SCHED. Enable fair_server with parameters equivalent to RT throttling. Signed-off-by:
Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by:
"Vineeth Pillai (Google)" <vineeth@bitbyteword.org> Signed-off-by:
Juri Lelli <juri.lelli@redhat.com> Link: https://lore.kernel.org/r/14d562db55df5c3c780d91940743acb166895ef7.1716811044.git.bristot@kernel.org
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Joel Fernandes (Google) authored
* Use simple CFS pick_task for DL pick_task DL server's pick_task calls CFS's pick_next_task_fair(), this is wrong because core scheduling's pick_task only calls CFS's pick_task() for evaluation / checking of the CFS task (comparing across CPUs), not for actually affirmatively picking the next task. This causes RB tree corruption issues in CFS that were found by syzbot. * Make pick_task_fair clear DL server A DL task pick might set ->dl_server, but it is possible the task will never run (say the other HT has a stop task). If the CFS task is picked in the future directly (say without DL server), ->dl_server will be set. So clear it in pick_task_fair(). This fixes the KASAN issue reported by syzbot in set_next_entity(). (DL refactoring suggestions by Vineeth Pillai). Reported-by:
Suleiman Souhlal <suleiman@google.com> Signed-off-by:
"Joel Fernandes (Google)" <joel@joelfernandes.org> Signed-off-by:
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Joel Fernandes (Google) authored
In core scheduling, a DL server pick (which is CFS task) should be given higher priority than tasks in other classes. Not doing so causes CFS starvation. A kselftest is added later to demonstrate this. A CFS task that is competing with RT tasks can be completely starved without this and the DL server's boosting completely ignored. Fix these problems. Reported-by:
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Daniel Bristot de Oliveira authored
Add an interface for fair server setup on debugfs. Each CPU has two files under /debug/sched/fair_server/cpu{ID}: - runtime: set runtime in ns - period: set period in ns This then leaves /proc/sys/kernel/sched_rt_{period,runtime}_us to set bounds on admission control. The interface also add the server to the dl bandwidth accounting. Signed-off-by: -
Daniel Bristot de Oliveira authored
Among the motivations for the DL servers is the real-time throttling mechanism. This mechanism works by throttling the rt_rq after running for a long period without leaving space for fair tasks. The base dl server avoids this problem by boosting fair tasks instead of throttling the rt_rq. The point is that it boosts without waiting for potential starvation, causing some non-intuitive cases. For example, an IRQ dispatches two tasks on an idle system, a fair and an RT. The DL server will be activated, running the fair task before the RT one. This problem can be avoided by deferring the dl server activation. By setting the defer option, the dl_server will dispatch an SCHED_DEADLINE reservation with replenished runtime, but throttled. The dl_timer will be set for the defer time at (period - runtime) ns from start time. Thus boosting the fair rq at defer time. If the fair scheduler has the opportunity to run while waiting for defer time, the dl server runtime will be consumed. If the runtime is completely consumed before the defer time, the server will be replenished while still in a throttled state. Then, the dl_timer will be reset to the new defer time If the fair server reaches the defer time without consuming its runtime, the server will start running, following CBS rules (thus without breaking SCHED_DEADLINE). Then the server will continue the running state (without deferring) until it fair tasks are able to execute as regular fair scheduler (end of the starvation). Signed-off-by:
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Peter Zijlstra authored
Use deadline servers to service fair tasks. This patch adds a fair_server deadline entity which acts as a container for fair entities and can be used to fix starvation when higher priority (wrt fair) tasks are monopolizing CPU(s). Signed-off-by:
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Youssef Esmat authored
In case the previous pick was a DL server pick, ->dl_server might be set. Clear it in the fast path as well. Fixes: 63ba8422 ("sched/deadline: Introduce deadline servers") Signed-off-by:
Youssef Esmat <youssefesmat@google.com> Signed-off-by:
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Joel Fernandes (Google) authored
Paths using put_prev_task_balance() need to do a pick shortly after. Make sure they also clear the ->dl_server on prev as a part of that. Fixes: 63ba8422 ("sched/deadline: Introduce deadline servers") Signed-off-by:
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Daniel Bristot de Oliveira authored
Add an explanation for the newly added variable. Fixes: 63ba8422 ("sched/deadline: Introduce deadline servers") Signed-off-by:
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Tianchen Ding authored
Consider the following cgroup: root | ------------------------ | | normal_cgroup idle_cgroup | | SCHED_IDLE task_A SCHED_NORMAL task_B According to the cgroup hierarchy, A should preempt B. But current check_preempt_wakeup_fair() treats cgroup se and task separately, so B will preempt A unexpectedly. Unify the wakeup logic by {c,p}se_is_idle only. This makes SCHED_IDLE of a task a relative policy that is effective only within its own cgroup, similar to the behavior of NICE. Also fix se_is_idle() definition when !CONFIG_FAIR_GROUP_SCHED. Fixes: 30400039 ("sched: Cgroup SCHED_IDLE support") Signed-off-by:Tianchen Ding <dtcccc@linux.alibaba.com> Signed-off-by:
Josh Don <joshdon@google.com> Reviewed-by:
Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/20240626023505.1332596-1-dtcccc@linux.alibaba.com
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Phil Auld authored
As a hedge against unexpected user issues commit 88c56cfe ("sched/fair: Block nohz tick_stop when cfs bandwidth in use") included a scheduler feature to disable the new functionality. It's been a few releases (v6.6) and no screams, so remove it. Signed-off-by:
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Chuyi Zhou authored
nr_spread_over tracks the number of instances where the difference between a scheduling entity's virtual runtime and the minimum virtual runtime in the runqueue exceeds three times the scheduler latency, indicating significant disparity in task scheduling. Commit that removed its usage: 5e963f2b: sched/fair: Commit to EEVDF cfs_rq->exec_clock was used to account for time spent executing tasks. Commit that removed its usage: 5d69eca5 sched: Unify runtime accounting across classes cfs_rq::nr_spread_over and cfs_rq::exec_clock are not used anymore in eevdf. Remove them from struct cfs_rq. Signed-off-by:
Chuyi Zhou <zhouchuyi@bytedance.com> Signed-off-by:
Vishal Chourasia <vishalc@linux.ibm.com> Link: https://lore.kernel.org/r/20240717143342.593262-1-zhouchuyi@bytedance.com
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Peilin He authored
Background ========== When repeated migrate_disable() calls are made with missing the corresponding migrate_enable() calls, there is a risk of 'migration_disabled' going upper overflow because 'migration_disabled' is a type of unsigned short whose max value is 65535. In PREEMPT_RT kernel, if 'migration_disabled' goes upper overflow, it may make the migrate_disable() ineffective within local_lock_irqsave(). This is because, during the scheduling procedure, the value of 'migration_disabled' will be checked, which can trigger CPU migration. Consequently, the count of 'rcu_read_lock_nesting' may leak due to local_lock_irqsave() and local_unlock_irqrestore() occurring on different CPUs. Usecase ======== For example, When I developed a driver, I encountered a warning like "WARNING: CPU: 4 PID: 260 at kernel/rcu/tree_plugin.h:315 rcu_note_context_switch+0xa8/0x4e8" warning. It took me half a month to locate this issue. Ultimately, I discovered that the lack of upper overflow detection mechanism in migrate_disable() was the root cause, leading to a significant amount of time spent on problem localization. If the upper overflow detection mechanism was added to migrate_disable(), the root cause could be very quickly and easily identified. Effect ====== Using WARN_ON_ONCE() to check if 'migration_disabled' is upper overflow can help developers identify the issue quickly. Suggested-by:
xu xin <xu.xin16@zte.com.cn> Signed-off-by:
Yunkai Zhang <zhang.yunkai@zte.com.cn> Reviewed-by:
Qiang Tu <tu.qiang35@zte.com.cn> Reviewed-by:
Kun Jiang <jiang.kun2@zte.com.cn> Reviewed-by:
Fan Yu <fan.yu9@zte.com.cn> Link: https://lkml.kernel.org/r/20240716104244764N2jD8gnBpnsLjCDnQGQ8c@zte.com.cn
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Zhang Qiao authored
When creating a new task, we initialize vruntime of the newly task at sched_cgroup_fork(). However, the timing of executing this action is too early and may not be accurate. Because it uses current CPU to init the vruntime, but the new task actually runs on the cpu which be assigned at wake_up_new_task(). To optimize this case, we pass ENQUEUE_INITIAL flag to activate_task() in wake_up_new_task(), in this way, when place_entity is called in enqueue_entity(), the vruntime of the new task will be initialized. In addition, place_entity() in task_fork_fair() was introduced for two reasons: 1. Previously, the __enqueue_entity() was in task_new_fair(), in order to provide vruntime for enqueueing the newly task, the vruntime assignment equation "se->vruntime = cfs_rq->min_vruntime" was introduced by commit e9acbff6 ("sched: introduce se->vruntime"). This is the initial state of place_entity(). 2. commit 4d78e7b6 ("sched: new task placement for vruntime") added child_runs_first task placement feature which based on vruntime, this also requires the new task's vruntime value. After removing the child_runs_first and enqueue_entity() from task_fork_fair(), this place_entity() no longer makes sense, so remove it also. Signed-off-by:
Zhang Qiao <zhangqiao22@huawei.com> Signed-off-by:
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Yang Yingliang authored
If cpuset_cpu_inactive() fails, set_rq_online() need be called to rollback. Fixes: 120455c5 ("sched: Fix hotplug vs CPU bandwidth control") Cc: stable@kernel.org Signed-off-by:
Yang Yingliang <yangyingliang@huawei.com> Signed-off-by:
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Yang Yingliang authored
Introduce sched_set_rq_on/offline() helper, so it can be called in normal or error path simply. No functional changed. Cc: stable@kernel.org Signed-off-by:
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Yang Yingliang authored
I got the following warn report while doing stress test: jump label: negative count! WARNING: CPU: 3 PID: 38 at kernel/jump_label.c:263 static_key_slow_try_dec+0x9d/0xb0 Call Trace: <TASK> __static_key_slow_dec_cpuslocked+0x16/0x70 sched_cpu_deactivate+0x26e/0x2a0 cpuhp_invoke_callback+0x3ad/0x10d0 cpuhp_thread_fun+0x3f5/0x680 smpboot_thread_fn+0x56d/0x8d0 kthread+0x309/0x400 ret_from_fork+0x41/0x70 ret_from_fork_asm+0x1b/0x30 </TASK> Because when cpuset_cpu_inactive() fails in sched_cpu_deactivate(), the cpu offline failed, but sched_smt_present is decremented before calling sched_cpu_deactivate(), it leads to unbalanced dec/inc, so fix it by incrementing sched_smt_present in the error path. Fixes: c5511d03 ("sched/smt: Make sched_smt_present track topology") Cc: stable@kernel.org Signed-off-by:
Chen Yu <yu.c.chen@intel.com> Reviewed-by:
Tim Chen <tim.c.chen@linux.intel.com> Link: https://lore.kernel.org/r/20240703031610.587047-3-yangyingliang@huaweicloud.com
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