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2024-08-23hrtimer: Use and report correct timerslack values for realtime tasksFelix Moessbauer
The timerslack_ns setting is used to specify how much the hardware timers should be delayed, to potentially dispatch multiple timers in a single interrupt. This is a performance optimization. Timers of realtime tasks (having a realtime scheduling policy) should not be delayed. This logic was inconsitently applied to the hrtimers, leading to delays of realtime tasks which used timed waits for events (e.g. condition variables). Due to the downstream override of the slack for rt tasks, the procfs reported incorrect (non-zero) timerslack_ns values. This is changed by setting the timer_slack_ns task attribute to 0 for all tasks with a rt policy. By that, downstream users do not need to specially handle rt tasks (w.r.t. the slack), and the procfs entry shows the correct value of "0". Setting non-zero slack values (either via procfs or PR_SET_TIMERSLACK) on tasks with a rt policy is ignored, as stated in "man 2 PR_SET_TIMERSLACK": Timer slack is not applied to threads that are scheduled under a real-time scheduling policy (see sched_setscheduler(2)). The special handling of timerslack on rt tasks in downstream users is removed as well. Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/all/20240814121032.368444-2-felix.moessbauer@siemens.com
2024-08-20sched_ext: Allow dequeue_task_scx to failYipeng Zou
Since dequeue_task() allowed to fail, there is a compile error: kernel/sched/ext.c:3630:19: error: initialization of ‘bool (*)(struct rq*, struct task_struct *, int)’ {aka ‘_Bool (*)(struct rq *, struct task_struct *, int)’} from incompatible pointer type ‘void (*)(struct rq*, struct task_struct *, int)’ 3630 | .dequeue_task = dequeue_task_scx, | ^~~~~~~~~~~~~~~~ Allow dequeue_task_scx to fail too. Fixes: 863ccdbb918a ("sched: Allow sched_class::dequeue_task() to fail") Signed-off-by: Yipeng Zou <zouyipeng@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2024-08-20Merge branch 'tip/sched/core' into for-6.12Tejun Heo
To receive 863ccdbb918a ("sched: Allow sched_class::dequeue_task() to fail") which makes sched_class.dequeue_task() return bool instead of void. This leads to compile breakage and will be fixed by a follow-up patch. Signed-off-by: Tejun Heo <tj@kernel.org>
2024-08-20softirq: Remove unused 'action' parameter from action callbackCaleb Sander Mateos
When soft interrupt actions are called, they are passed a pointer to the struct softirq action which contains the action's function pointer. This pointer isn't useful, as the action callback already knows what function it is. And since each callback handles a specific soft interrupt, the callback also knows which soft interrupt number is running. No soft interrupt action callback actually uses this parameter, so remove it from the function pointer signature. This clarifies that soft interrupt actions are global routines and makes it slightly cheaper to call them. Signed-off-by: Caleb Sander Mateos <csander@purestorage.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Jens Axboe <axboe@kernel.dk> Link: https://lore.kernel.org/all/20240815171549.3260003-1-csander@purestorage.com
2024-08-17sched/eevdf: Propagate min_slice up the cgroup hierarchyPeter Zijlstra
In the absence of an explicit cgroup slice configureation, make mixed slice length work with cgroups by propagating the min_slice up the hierarchy. This ensures the cgroup entity gets timely service to service its entities that have this timing constraint set on them. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.948188417@infradead.org
2024-08-17sched/eevdf: Use sched_attr::sched_runtime to set request/slice suggestionPeter Zijlstra
Allow applications to directly set a suggested request/slice length using sched_attr::sched_runtime. The implementation clamps the value to: 0.1[ms] <= slice <= 100[ms] which is 1/10 the size of HZ=1000 and 10 times the size of HZ=100. Applications should strive to use their periodic runtime at a high confidence interval (95%+) as the target slice. Using a smaller slice will introduce undue preemptions, while using a larger value will increase latency. For all the following examples assume a scheduling quantum of 8, and for consistency all examples have W=4: {A,B,C,D}(w=1,r=8): ABCD... +---+---+---+--- t=0, V=1.5 t=1, V=3.5 A |------< A |------< B |------< B |------< C |------< C |------< D |------< D |------< ---+*------+-------+--- ---+--*----+-------+--- t=2, V=5.5 t=3, V=7.5 A |------< A |------< B |------< B |------< C |------< C |------< D |------< D |------< ---+----*--+-------+--- ---+------*+-------+--- Note: 4 identical tasks in FIFO order ~~~ {A,B}(w=1,r=16) C(w=2,r=16) AACCBBCC... +---+---+---+--- t=0, V=1.25 t=2, V=5.25 A |--------------< A |--------------< B |--------------< B |--------------< C |------< C |------< ---+*------+-------+--- ---+----*--+-------+--- t=4, V=8.25 t=6, V=12.25 A |--------------< A |--------------< B |--------------< B |--------------< C |------< C |------< ---+-------*-------+--- ---+-------+---*---+--- Note: 1 heavy task -- because q=8, double r such that the deadline of the w=2 task doesn't go below q. Note: observe the full schedule becomes: W*max(r_i/w_i) = 4*2q = 8q in length. Note: the period of the heavy task is half the full period at: W*(r_i/w_i) = 4*(2q/2) = 4q ~~~ {A,C,D}(w=1,r=16) B(w=1,r=8): BAACCBDD... +---+---+---+--- t=0, V=1.5 t=1, V=3.5 A |--------------< A |---------------< B |------< B |------< C |--------------< C |--------------< D |--------------< D |--------------< ---+*------+-------+--- ---+--*----+-------+--- t=3, V=7.5 t=5, V=11.5 A |---------------< A |---------------< B |------< B |------< C |--------------< C |--------------< D |--------------< D |--------------< ---+------*+-------+--- ---+-------+--*----+--- t=6, V=13.5 A |---------------< B |------< C |--------------< D |--------------< ---+-------+----*--+--- Note: 1 short task -- again double r so that the deadline of the short task won't be below q. Made B short because its not the leftmost task, but is eligible with the 0,1,2,3 spread. Note: like with the heavy task, the period of the short task observes: W*(r_i/w_i) = 4*(1q/1) = 4q ~~~ A(w=1,r=16) B(w=1,r=8) C(w=2,r=16) BCCAABCC... +---+---+---+--- t=0, V=1.25 t=1, V=3.25 A |--------------< A |--------------< B |------< B |------< C |------< C |------< ---+*------+-------+--- ---+--*----+-------+--- t=3, V=7.25 t=5, V=11.25 A |--------------< A |--------------< B |------< B |------< C |------< C |------< ---+------*+-------+--- ---+-------+--*----+--- t=6, V=13.25 A |--------------< B |------< C |------< ---+-------+----*--+--- Note: 1 heavy and 1 short task -- combine them all. Note: both the short and heavy task end up with a period of 4q ~~~ A(w=1,r=16) B(w=2,r=16) C(w=1,r=8) BBCAABBC... +---+---+---+--- t=0, V=1 t=2, V=5 A |--------------< A |--------------< B |------< B |------< C |------< C |------< ---+*------+-------+--- ---+----*--+-------+--- t=3, V=7 t=5, V=11 A |--------------< A |--------------< B |------< B |------< C |------< C |------< ---+------*+-------+--- ---+-------+--*----+--- t=7, V=15 A |--------------< B |------< C |------< ---+-------+------*+--- Note: as before but permuted ~~~ From all this it can be deduced that, for the steady state: - the total period (P) of a schedule is: W*max(r_i/w_i) - the average period of a task is: W*(r_i/w_i) - each task obtains the fair share: w_i/W of each full period P Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.842834421@infradead.org
2024-08-17sched/eevdf: Allow shorter slices to wakeup-preemptPeter Zijlstra
Part of the reason to have shorter slices is to improve responsiveness. Allow shorter slices to preempt longer slices on wakeup. Task | Runtime ms | Switches | Avg delay ms | Max delay ms | Sum delay ms | 100ms massive_intr 500us cyclictest NO_PREEMPT_SHORT 1 massive_intr:(5) | 846018.956 ms | 779188 | avg: 0.273 ms | max: 58.337 ms | sum:212545.245 ms | 2 massive_intr:(5) | 853450.693 ms | 792269 | avg: 0.275 ms | max: 71.193 ms | sum:218263.588 ms | 3 massive_intr:(5) | 843888.920 ms | 771456 | avg: 0.277 ms | max: 92.405 ms | sum:213353.221 ms | 1 chromium-browse:(8) | 53015.889 ms | 131766 | avg: 0.463 ms | max: 36.341 ms | sum:60959.230 ms | 2 chromium-browse:(8) | 53864.088 ms | 136962 | avg: 0.480 ms | max: 27.091 ms | sum:65687.681 ms | 3 chromium-browse:(9) | 53637.904 ms | 132637 | avg: 0.481 ms | max: 24.756 ms | sum:63781.673 ms | 1 cyclictest:(5) | 12615.604 ms | 639689 | avg: 0.471 ms | max: 32.272 ms | sum:301351.094 ms | 2 cyclictest:(5) | 12511.583 ms | 642578 | avg: 0.448 ms | max: 44.243 ms | sum:287632.830 ms | 3 cyclictest:(5) | 12545.867 ms | 635953 | avg: 0.475 ms | max: 25.530 ms | sum:302374.658 ms | 100ms massive_intr 500us cyclictest PREEMPT_SHORT 1 massive_intr:(5) | 839843.919 ms | 837384 | avg: 0.264 ms | max: 74.366 ms | sum:221476.885 ms | 2 massive_intr:(5) | 852449.913 ms | 845086 | avg: 0.252 ms | max: 68.162 ms | sum:212595.968 ms | 3 massive_intr:(5) | 839180.725 ms | 836883 | avg: 0.266 ms | max: 69.742 ms | sum:222812.038 ms | 1 chromium-browse:(11) | 54591.481 ms | 138388 | avg: 0.458 ms | max: 35.427 ms | sum:63401.508 ms | 2 chromium-browse:(8) | 52034.541 ms | 132276 | avg: 0.436 ms | max: 31.826 ms | sum:57732.958 ms | 3 chromium-browse:(8) | 55231.771 ms | 141892 | avg: 0.469 ms | max: 27.607 ms | sum:66538.697 ms | 1 cyclictest:(5) | 13156.391 ms | 667412 | avg: 0.373 ms | max: 38.247 ms | sum:249174.502 ms | 2 cyclictest:(5) | 12688.939 ms | 665144 | avg: 0.374 ms | max: 33.548 ms | sum:248509.392 ms | 3 cyclictest:(5) | 13475.623 ms | 669110 | avg: 0.370 ms | max: 37.819 ms | sum:247673.390 ms | As per the numbers the, this makes cyclictest (short slice) it's max-delay more consistent and consistency drops the sum-delay. The trade-off is that the massive_intr (long slice) gets more context switches and a slight increase in sum-delay. Chunxin contributed did_preempt_short() where a task that lost slice protection from PREEMPT_SHORT gets rescheduled once it becomes in-eligible. [mike: numbers] Co-Developed-by: Chunxin Zang <zangchunxin@lixiang.com> Signed-off-by: Chunxin Zang <zangchunxin@lixiang.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Mike Galbraith <umgwanakikbuti@gmail.com> Link: https://lkml.kernel.org/r/20240727105030.735459544@infradead.org
2024-08-17sched/fair: Avoid re-setting virtual deadline on 'migrations'Peter Zijlstra
During OSPM24 Youssef noted that migrations are re-setting the virtual deadline. Notably everything that does a dequeue-enqueue, like setting nice, changing preferred numa-node, and a myriad of other random crap, will cause this to happen. This shouldn't be. Preserve the relative virtual deadline across such dequeue/enqueue cycles. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.625119246@infradead.org
2024-08-17sched/eevdf: Fixup PELT vs DELAYED_DEQUEUEPeter Zijlstra
Note that tasks that are kept on the runqueue to burn off negative lag, are not in fact runnable anymore, they'll get dequeued the moment they get picked. As such, don't count this time towards runnable. Thanks to Valentin for spotting I had this backwards initially. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.514088302@infradead.org
2024-08-17sched/fair: Implement DELAY_ZEROPeter Zijlstra
'Extend' DELAY_DEQUEUE by noting that since we wanted to dequeued them at the 0-lag point, truncate lag (eg. don't let them earn positive lag). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.403750550@infradead.org
2024-08-17sched/fair: Implement delayed dequeuePeter Zijlstra
Extend / fix 86bfbb7ce4f6 ("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: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.226163742@infradead.org
2024-08-17sched: Teach dequeue_task() about special task statesPeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105030.110439521@infradead.org
2024-08-17sched/fair: Implement ENQUEUE_DELAYEDPeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.888107381@infradead.org
2024-08-17sched/fair: Prepare pick_next_task() for delayed dequeuePeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.747330118@infradead.org
2024-08-17sched/fair: Prepare exit/cleanup paths for delayed_dequeuePeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.631948434@infradead.org
2024-08-17sched/fair: Assert {set_next,put_prev}_entity() are properly balancedPeter Zijlstra
Just a little sanity test.. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.486423066@infradead.org
2024-08-17sched/uclamg: Handle delayed dequeuePeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.315205425@infradead.org
2024-08-17sched: Prepare generic code for delayed dequeuePeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.200000445@infradead.org
2024-08-17sched: Split DEQUEUE_SLEEP from deactivate_task()Peter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.086192709@infradead.org
2024-08-17sched/fair: Re-organize dequeue_task_fair()Peter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.977256873@infradead.org
2024-08-17sched: Allow sched_class::dequeue_task() to failPeter Zijlstra
Change the function signature of sched_class::dequeue_task() to return a boolean, allowing future patches to 'fail' dequeue. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.864630153@infradead.org
2024-08-17sched/fair: Unify pick_{,next_}_task_fair()Peter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.725062368@infradead.org
2024-08-17sched/fair: Cleanup pick_task_fair()'s currPeter Zijlstra
With 4c456c9ad334 ("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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.614707623@infradead.org
2024-08-17sched/fair: Cleanup pick_task_fair() vs throttlePeter Zijlstra
Per 54d27365cae8 ("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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Ben Segall <bsegall@google.com> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.501679876@infradead.org
2024-08-17sched/eevdf: Remove min_vruntime_copyPeter Zijlstra
Since commit e8f331bcc270 ("sched/smp: Use lag to simplify cross-runqueue placement") the min_vruntime_copy is no longer used. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.395297941@infradead.org
2024-08-17sched/eevdf: Add feature commentsPeter Zijlstra
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105028.287790895@infradead.org
2024-08-15rcu: Let dump_cpu_task() be used without preemption disabledRyo Takakura
The commit 2d7f00b2f0130 ("rcu: Suppress smp_processor_id() complaint in synchronize_rcu_expedited_wait()") disabled preemption around dump_cpu_task() to suppress warning on its usage within preemtible context. Calling dump_cpu_task() doesn't required to be in non-preemptible context except for suppressing the smp_processor_id() warning. As the smp_processor_id() is evaluated along with in_hardirq() to check if it's in interrupt context, this patch removes the need for its preemtion disablement by reordering the condition so that smp_processor_id() only gets evaluated when it's in interrupt context. Signed-off-by: Ryo Takakura <takakura@valinux.co.jp> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
2024-08-13sched_ext: Don't use double locking to migrate tasks across CPUsTejun Heo
consume_remote_task() and dispatch_to_local_dsq() use move_task_to_local_dsq() to migrate the task to the target CPU. Currently, move_task_to_local_dsq() expects the caller to lock both the source and destination rq's. While this may save a few lock operations while the rq's are not contended, under contention, the double locking can exacerbate the situation significantly (refer to the linked message below). Update the migration path so that double locking is not used. move_task_to_local_dsq() now expects the caller to be locking the source rq, drops it and then acquires the destination rq lock. Code is simpler this way and, on a 2-way NUMA machine w/ Xeon Gold 6138, 'hackbench 100 thread 5000` shows ~3% improvement with scx_simple. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20240806082716.GP37996@noisy.programming.kicks-ass.net Acked-by: David Vernet <void@manifault.com>
2024-08-13sched_ext: define missing cfi stubs for sched_extManu Bretelle
`__bpf_ops_sched_ext_ops` was missing the initialization of some struct attributes. With https://lore.kernel.org/all/20240722183049.2254692-4-martin.lau@linux.dev/ every single attributes need to be initialized programs (like scx_layered) will fail to load. 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_init not found in kernel, skipping it as it's set to zero 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_exit not found in kernel, skipping it as it's set to zero 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_prep_move not found in kernel, skipping it as it's set to zero 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_move not found in kernel, skipping it as it's set to zero 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_cancel_move not found in kernel, skipping it as it's set to zero 05:26:48 [INFO] libbpf: struct_ops layered: member cgroup_set_weight not found in kernel, skipping it as it's set to zero 05:26:48 [WARN] libbpf: prog 'layered_dump': BPF program load failed: unknown error (-524) 05:26:48 [WARN] libbpf: prog 'layered_dump': -- BEGIN PROG LOAD LOG -- attach to unsupported member dump of struct sched_ext_ops processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0 -- END PROG LOAD LOG -- 05:26:48 [WARN] libbpf: prog 'layered_dump': failed to load: -524 05:26:48 [WARN] libbpf: failed to load object 'bpf_bpf' 05:26:48 [WARN] libbpf: failed to load BPF skeleton 'bpf_bpf': -524 Error: Failed to load BPF program Signed-off-by: Manu Bretelle <chantr4@gmail.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2024-08-08sched_ext: Improve logging around enable/disableTejun Heo
sched_ext currently doesn't generate messages when the BPF scheduler is enabled and disabled unless there are errors. It is useful to have paper trail. Improve logging around enable/disable: - Generate info messages on enable and non-error disable. - Update error exit message formatting so that it's consistent with non-error message. Also, prefix ei->msg with the BPF scheduler's name to make it clear where the message is coming from. - Shorten scx_exit_reason() strings for SCX_EXIT_UNREG* for brevity and consistency. v2: Use pr_*() instead of KERN_* consistently. (David) Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Phil Auld <pauld@redhat.com> Reviewed-by: Phil Auld <pauld@redhat.com> Acked-by: David Vernet <void@manifault.com>
2024-08-08sched_ext: Make scx_rq_online() also test cpu_active() in addition to ↵Tejun Heo
SCX_RQ_ONLINE scx_rq_online() currently only tests SCX_RQ_ONLINE. This isn't fully correct - e.g. consume_dispatch_q() uses task_run_on_remote_rq() which tests scx_rq_online() to see whether the current rq can run the task, and, if so, calls consume_remote_task() to migrate the task to @rq. While the test itself was done while locking @rq, @rq can be temporarily unlocked by consume_remote_task() and nothing prevents SCX_RQ_ONLINE from going offline before the migration takes place. To address the issue, add cpu_active() test to scx_rq_online(). There is a synchronize_rcu() between cpu_active() being cleared and the rq going offline, so if an on-going scheduling operation sees cpu_active(), the associated rq is guaranteed to not go offline until the scheduling operation is complete. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: 60c27fb59f6c ("sched_ext: Implement sched_ext_ops.cpu_online/offline()") Acked-by: David Vernet <void@manifault.com>
2024-08-08sched_ext: Fix unsafe list iteration in process_ddsp_deferred_locals()Tejun Heo
process_ddsp_deferred_locals() executes deferred direct dispatches to the local DSQs of remote CPUs. It iterates the tasks on rq->scx.ddsp_deferred_locals list, removing and calling dispatch_to_local_dsq() on each. However, the list is protected by the rq lock that can be dropped by dispatch_to_local_dsq() temporarily, so the list can be modified during the iteration, which can lead to oopses and other failures. Fix it by popping from the head of the list instead of iterating the list. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: 5b26f7b920f7 ("sched_ext: Allow SCX_DSQ_LOCAL_ON for direct dispatches") Acked-by: David Vernet <void@manifault.com>
2024-08-07sched/rt: Rename realtime_{prio, task}() to rt_or_dl_{prio, task}()Qais Yousef
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: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20240610192018.1567075-4-qyousef@layalina.io
2024-08-07sched/rt: Clean up usage of rt_task()Qais Yousef
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: Qais Yousef <qyousef@layalina.io> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Phil Auld <pauld@redhat.com> Reviewed-by: "Steven Rostedt (Google)" <rostedt@goodmis.org> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.kernel.org/r/20240610192018.1567075-2-qyousef@layalina.io
2024-08-07sched/debug: Fix fair_server_period_max valueDan Carpenter
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: d741f297bcea ("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: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain
2024-08-07sched/fair: Make balance_fair() test sched_fair_runnable() instead of ↵Tejun Heo
rq->nr_running 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: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-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
2024-08-06sched_ext: Make task_can_run_on_remote_rq() use common task_allowed_on_cpu()Tejun Heo
task_can_run_on_remote_rq() is similar to is_cpu_allowed() but there are subtle differences. It currently open codes all the tests. This is cumbersome to understand and error-prone in case the intersecting tests need to be updated. Factor out the common part - testing whether the task is allowed on the CPU at all regardless of the CPU state - into task_allowed_on_cpu() and make both is_cpu_allowed() and SCX's task_can_run_on_remote_rq() use it. As the code is now linked between the two and each contains only the extra tests that differ between them, it's less error-prone when the conditions need to be updated. Also, improve the comment to explain why they are different. v2: Replace accidental "extern inline" with "static inline" (Peter). Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-06sched_ext: Improve comment on idle_sched_class exception in ↵Tejun Heo
scx_task_iter_next_locked() scx_task_iter_next_locked() skips tasks whose sched_class is idle_sched_class. While it has a short comment explaining why it's testing the sched_class directly isntead of using is_idle_task(), the comment doesn't sufficiently explain what's going on and why. Improve the comment. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-06sched_ext: Simplify UP support by enabling sched_class->balance() in UPTejun Heo
On SMP, SCX performs dispatch from sched_class->balance(). As balance() was not available in UP, it instead called the internal balance function from put_prev_task_scx() and pick_next_task_scx() to emulate the effect, which is rather nasty. Enabling sched_class->balance() on UP shouldn't cause any meaningful overhead. Enable balance() on UP and drop the ugly workaround. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-06sched_ext: Use update_curr_common() in update_curr_scx()Tejun Heo
update_curr_scx() is open coding runtime updates. Use update_curr_common() instead and avoid unnecessary deviations. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-06sched_ext: Add scx_enabled() test to @start_class promotion in ↵Tejun Heo
put_prev_task_balance() SCX needs its balance() invoked even when waking up from a lower priority sched class (idle) and put_prev_task_balance() thus has the logic to promote @start_class if it's lower than ext_sched_class. This is only needed when SCX is enabled. Add scx_enabled() test to avoid unnecessary overhead when SCX is disabled. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-06sched_ext: Simplify scx_can_stop_tick() invocation in sched_can_stop_tick()Tejun Heo
The way sched_can_stop_tick() used scx_can_stop_tick() was rather confusing and the behavior wasn't ideal when SCX is enabled in partial mode. Simplify it so that: - scx_can_stop_tick() can say no if scx_enabled(). - CFS tests rq->cfs.nr_running > 1 instead of rq->nr_running. This is easier to follow and leads to the correct answer whether SCX is disabled, enabled in partial mode or all tasks are switched to SCX. Peter, note that this is a bit different from your suggestion where sched_can_stop_tick() unconditionally returns scx_can_stop_tick() iff scx_switched_all(). The problem is that in partial mode, tick can be stopped when there is only one SCX task even if the BPF scheduler didn't ask and isn't ready for it. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: David Vernet <void@manifault.com>
2024-08-04profiling: remove profile=sleep supportTetsuo Handa
The kernel sleep profile is no longer working due to a recursive locking bug introduced by commit 42a20f86dc19 ("sched: Add wrapper for get_wchan() to keep task blocked") Booting with the 'profile=sleep' kernel command line option added or executing # echo -n sleep > /sys/kernel/profiling after boot causes the system to lock up. Lockdep reports kthreadd/3 is trying to acquire lock: ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: get_wchan+0x32/0x70 but task is already holding lock: ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: try_to_wake_up+0x53/0x370 with the call trace being lock_acquire+0xc8/0x2f0 get_wchan+0x32/0x70 __update_stats_enqueue_sleeper+0x151/0x430 enqueue_entity+0x4b0/0x520 enqueue_task_fair+0x92/0x6b0 ttwu_do_activate+0x73/0x140 try_to_wake_up+0x213/0x370 swake_up_locked+0x20/0x50 complete+0x2f/0x40 kthread+0xfb/0x180 However, since nobody noticed this regression for more than two years, let's remove 'profile=sleep' support based on the assumption that nobody needs this functionality. Fixes: 42a20f86dc19 ("sched: Add wrapper for get_wchan() to keep task blocked") Cc: stable@vger.kernel.org # v5.16+ Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-08-04Merge branch 'sched/core' of ↵Tejun Heo
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into for-6.12 Pull tip/sched/core to resolve the following four conflicts. While 2-4 are simple context conflicts, 1 is a bit subtle and easy to resolve incorrectly. 1. 2c8d046d5d51 ("sched: Add normal_policy()") vs. faa42d29419d ("sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy") The former converts direct test on p->policy to use the helper normal_policy(). The latter moves the p->policy test to a different location. Resolve by converting the test on p->plicy in the new location to use normal_policy(). 2. a7a9fc549293 ("sched_ext: Add boilerplate for extensible scheduler class") vs. a110a81c52a9 ("sched/deadline: Deferrable dl server") Both add calls to put_prev_task_idle() and set_next_task_idle(). Simple context conflict. Resolve by taking changes from both. 3. a7a9fc549293 ("sched_ext: Add boilerplate for extensible scheduler class") vs. c245910049d0 ("sched/core: Add clearing of ->dl_server in put_prev_task_balance()") The former changes for_each_class() itertion to use for_each_active_class(). The latter moves away the adjacent dl_server handling code. Simple context conflict. Resolve by taking changes from both. 4. 60c27fb59f6c ("sched_ext: Implement sched_ext_ops.cpu_online/offline()") vs. 31b164e2e4af ("sched/smt: Introduce sched_smt_present_inc/dec() helper") 2f027354122f ("sched/core: Introduce sched_set_rq_on/offline() helper") The former adds scx_rq_deactivate() call. The latter two change code around it. Simple context conflict. Resolve by taking changes from both. Signed-off-by: Tejun Heo <tj@kernel.org>
2024-08-02sched_ext: Allow p->scx.disallow only while loadingTejun Heo
From 1232da7eced620537a78f19c8cf3d4a3508e2419 Mon Sep 17 00:00:00 2001 From: Tejun Heo <tj@kernel.org> Date: Wed, 31 Jul 2024 09:14:52 -1000 p->scx.disallow provides a way for the BPF scheduler to reject certain tasks from attaching. It's currently allowed for both the load and fork paths; however, the latter doesn't actually work as p->sched_class is already set by the time scx_ops_init_task() is called during fork. This is a convenience feature which is mostly useful from the load path anyway. Allow it only from the load path. v2: Trigger scx_ops_error() iff @p->policy == SCHED_EXT to make it a bit easier for the BPF scheduler (David). Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: "Zhangqiao (2012 lab)" <zhangqiao22@huawei.com> Link: http://lkml.kernel.org/r/20240711110720.1285-1-zhangqiao22@huawei.com Fixes: 7bb6f0810ecf ("sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT") Acked-by: David Vernet <void@manifault.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2024-08-01sched_ext: Build fix on !CONFIG_STACKTRACE[_SUPPORT]Tejun Heo
scx_dump_task() uses stack_trace_save_tsk() which is only available when CONFIG_STACKTRACE. Make CONFIG_SCHED_CLASS_EXT select CONFIG_STACKTRACE if the support is available and skip capturing stack trace if !CONFIG_STACKTRACE. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202407161844.reewQQrR-lkp@intel.com/ Acked-by: David Vernet <void@manifault.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2024-07-31scx: Allow calling sleepable kfuncs from BPF_PROG_TYPE_SYSCALLDavid Vernet
We currently only allow calling sleepable scx kfuncs (i.e. scx_bpf_create_dsq()) from BPF_PROG_TYPE_STRUCT_OPS progs. The idea here was that we'd never have to call scx_bpf_create_dsq() outside of a sched_ext struct_ops callback, but that might not actually be true. For example, a scheduler could do something like the following: 1. Open and load (not yet attach) a scheduler skel 2. Synchronously call into a BPF_PROG_TYPE_SYSCALL prog from user space. For example, to initialize an LLC domain, or some other global, read-only state. 3. Attach the skel, which actually enables the scheduler The advantage of doing this is that it can preclude having to do pretty ugly boilerplate like initializing a read-only, statically sized array of u64[]'s which the kernel consumes literally once at init time to then create struct bpf_cpumask objects which are actually queried at runtime. Doing the above is already possible given that we can invoke core BPF kfuncs, such as bpf_cpumask_create(), from BPF_PROG_TYPE_SYSCALL progs. We already allow many scx kfuncs to be called from BPF_PROG_TYPE_SYSCALL progs (e.g. scx_bpf_kick_cpu()). Let's allow the sleepable kfuncs as well. Signed-off-by: David Vernet <void@manifault.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2024-07-30Merge tag 'v6.11-rc1' into for-6.12Tejun Heo
Linux 6.11-rc1
2024-07-29sched/fair: Cleanup fair_serverPeter Zijlstra
The throttle interaction made my brain hurt, make it consistently about 0 transitions of h_nr_running. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2024-07-29sched/rt: Remove default bandwidth controlPeter Zijlstra
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: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: "Vineeth Pillai (Google)" <vineeth@bitbyteword.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Juri Lelli <juri.lelli@redhat.com> Link: https://lore.kernel.org/r/14d562db55df5c3c780d91940743acb166895ef7.1716811044.git.bristot@kernel.org
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