- 19 Nov, 2020 2 commits
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Peter Zijlstra authored
Oleksandr reported hitting the WARN in the 'task_rq(p) != rq' branch of migration_cpu_stop(). Valentin noted that using cpu_of(rq) in that case is just plain wrong to begin with, since per the earlier branch that isn't the actual CPU of the task. Replace both instances of is_cpu_allowed() by a direct p->cpus_mask test using task_cpu(). Reported-by:
Oleksandr Natalenko <oleksandr@natalenko.name> Debugged-by:
Valentin Schneider <valentin.schneider@arm.com> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org>
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Valentin Schneider authored
Qian reported that some fuzzer issuing sched_setaffinity() ends up stuck on a wait_for_completion(). The problematic pattern seems to be: affine_move_task() // task_running() case stop_one_cpu(); wait_for_completion(&pending->done); Combined with, on the stopper side: migration_cpu_stop() // Task moved between unlocks and scheduling the stopper task_rq(p) != rq && // task_running() case dest_cpu >= 0 => no complete_all() This can happen with both PREEMPT and !PREEMPT, although !PREEMPT should be more likely to see this given the targeted task has a much bigger window to block and be woken up elsewhere before the stopper runs. Make migration_cpu_stop() always look at pending affinity requests; signal their completion if the stopper hits a rq mismatch but the task is still within its allowed mask. When Migrate-Disable isn't involved, this matches the previous set_cpus_allowed_ptr() vs migration_cpu_stop() behaviour. Fixes: 6d337eab ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Reported-by:Qian Cai <cai@redhat.com> Signed-off-by:
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- 10 Nov, 2020 24 commits
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Valentin Schneider authored
The CFS wakeup code will only ever go through EAS / its fast path on "regular" wakeups (i.e. not on forks or execs). These are currently gated by a check against 'sd_flag', which would be SD_BALANCE_WAKE at wakeup. However, we now have a flag that explicitly tells us whether a wakeup is a "regular" one, so hinge those conditions on that flag instead. Signed-off-by:
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Valentin Schneider authored
Only select_task_rq_fair() uses that parameter to do an actual domain search, other classes only care about what kind of wakeup is happening (fork, exec, or "regular") and thus just translate the flag into a wakeup type. WF_TTWU and WF_EXEC have just been added, use these along with WF_FORK to encode the wakeup types we care about. For select_task_rq_fair(), we can simply use the shiny new WF_flag : SD_flag mapping. Signed-off-by:
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Valentin Schneider authored
To remove the sd_flag parameter of select_task_rq(), we need another way of encoding wakeup types. There already is a WF_FORK flag, add the missing two. With that said, we still need an easy way to turn WF_foo into SD_bar (e.g. WF_TTWU into SD_BALANCE_WAKE). As suggested by Peter, let's make our lives easier and make them match exactly, and throw in some compile-time checks for good measure. Signed-off-by:
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Hui Su authored
Since ab93a4bc ("sched/fair: Remove distribute_running fromCFS bandwidth"), there is nothing to protect between raw_spin_lock_irqsave/store() in do_sched_cfs_slack_timer(). Signed-off-by:
Hui Su <sh_def@163.com> Signed-off-by:
Phil Auld <pauld@redhat.com> Reviewed-by:
Ben Segall <bsegall@google.com> Link: https://lkml.kernel.org/r/20201030144621.GA96974@rlk
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Peter Zijlstra authored
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Valentin Schneider authored
Signed-off-by:
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Valentin Schneider authored
migrate_disable(); set_cpus_allowed_ptr(current, {something excluding task_cpu(current)}); affine_move_task(); <-- never returns Signed-off-by: -
Peter Zijlstra authored
Ensure /proc/*/status doesn't print 'random' cpumasks due to migrate_disable(). Signed-off-by:
Daniel Bristot de Oliveira <bristot@redhat.com> Link: https://lkml.kernel.org/r/20201023102347.593984734@infradead.org
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Peter Zijlstra authored
In order to minimize the interference of migrate_disable() on lower priority tasks, which can be deprived of runtime due to being stuck below a higher priority task. Teach the RT/DL balancers to push away these higher priority tasks when a lower priority task gets selected to run on a freshly demoted CPU (pull). This adds migration interference to the higher priority task, but restores bandwidth to system that would otherwise be irrevocably lost. Without this it would be possible to have all tasks on the system stuck on a single CPU, each task preempted in a migrate_disable() section with a single high priority task running. This way we can still approximate running the M highest priority tasks on the system. Migrating the top task away is (ofcourse) still subject to migrate_disable() too, which means the lower task is subject to an interference equivalent to the worst case migrate_disable() section. Signed-off-by:
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Peter Zijlstra authored
There's a valid ->pi_lock recursion issue where the actual PI code tries to wake up the stop task. Make lockdep aware so it doesn't complain about this. Signed-off-by:
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Peter Zijlstra authored
We want migrate_disable() tasks to get PULLs in order for them to PUSH away the higher priority task. Signed-off-by:
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Peter Zijlstra authored
Replace a bunch of cpumask_any*() instances with cpumask_any*_distribute(), by injecting this little bit of random in cpu selection, we reduce the chance two competing balance operations working off the same lowest_mask pick the same CPU. Signed-off-by:
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Thomas Gleixner authored
On CPU unplug tasks which are in a migrate disabled region cannot be pushed to a different CPU until they returned to migrateable state. Account the number of tasks on a runqueue which are in a migrate disabled section and make the hotplug wait mechanism respect that. Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
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Peter Zijlstra authored
Concurrent migrate_disable() and set_cpus_allowed_ptr() has interesting features. We rely on set_cpus_allowed_ptr() to not return until the task runs inside the provided mask. This expectation is exported to userspace. This means that any set_cpus_allowed_ptr() caller must wait until migrate_enable() allows migrations. At the same time, we don't want migrate_enable() to schedule, due to patterns like: preempt_disable(); migrate_disable(); ... migrate_enable(); preempt_enable(); And: raw_spin_lock(&B); spin_unlock(&A); this means that when migrate_enable() must restore the affinity mask, it cannot wait for completion thereof. Luck will have it that that is exactly the case where there is a pending set_cpus_allowed_ptr(), so let that provide storage for the async stop machine. Much thanks to Valentin who used TLA+ most effective and found lots of 'interesting' cases. Signed-off-by:
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Peter Zijlstra authored
Add the base migrate_disable() support (under protest). While migrate_disable() is (currently) required for PREEMPT_RT, it is also one of the biggest flaws in the system. Notably this is just the base implementation, it is broken vs sched_setaffinity() and hotplug, both solved in additional patches for ease of review. Signed-off-by:
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Peter Zijlstra authored
Thread a u32 flags word through the *set_cpus_allowed*() callchain. This will allow adding behavioural tweaks for future users. Signed-off-by:
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Peter Zijlstra authored
Since we now migrate tasks away before DYING, we should also move bandwidth unthrottle, otherwise we can gain tasks from unthrottle after we expect all tasks to be gone already. Also; it looks like the RT balancers don't respect cpu_active() and instead rely on rq->online in part, complete this. This too requires we do set_rq_offline() earlier to match the cpu_active() semantics. (The bigger patch is to convert RT to cpu_active() entirely) Since set_rq_online() is called from sched_cpu_activate(), place set_rq_offline() in sched_cpu_deactivate(). Signed-off-by:
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Thomas Gleixner authored
With the new mechanism which kicks tasks off the outgoing CPU at the end of schedule() the situation on an outgoing CPU right before the stopper thread brings it down completely is: - All user tasks and all unbound kernel threads have either been migrated away or are not running and the next wakeup will move them to a online CPU. - All per CPU kernel threads, except cpu hotplug thread and the stopper thread have either been unbound or parked by the responsible CPU hotplug callback. That means that at the last step before the stopper thread is invoked the cpu hotplug thread is the last legitimate running task on the outgoing CPU. Add a final wait step right before the stopper thread is kicked which ensures that any still running tasks on the way to park or on the way to kick themself of the CPU are either sleeping or gone. This allows to remove the migrate_tasks() crutch in sched_cpu_dying(). If sched_cpu_dying() detects that there is still another running task aside of the stopper thread then it will explode with the appropriate fireworks. Signed-off-by:
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Peter Zijlstra authored
Don't rely on the scheduler to force break affinity for us -- it will stop doing that for per-cpu-kthreads. Signed-off-by:
Tejun Heo <tj@kernel.org> Reviewed-by:
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Thomas Gleixner authored
RT kernels need to ensure that all tasks which are not per CPU kthreads have left the outgoing CPU to guarantee that no tasks are force migrated within a migrate disabled section. There is also some desire to (ab)use fine grained CPU hotplug control to clear a CPU from active state to force migrate tasks which are not per CPU kthreads away for power control purposes. Add a mechanism which waits until all tasks which should leave the CPU after the CPU active flag is cleared have moved to a different online CPU. Signed-off-by:
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Peter Zijlstra authored
In preparation for migrate_disable(), make sure only per-cpu kthreads are allowed to run on !active CPUs. This is ran (as one of the very first steps) from the cpu-hotplug task which is a per-cpu kthread and completion of the hotplug operation only requires such tasks. This constraint enables the migrate_disable() implementation to wait for completion of all migrate_disable regions on this CPU at hotplug time without fear of any new ones starting. This replaces the unlikely(rq->balance_callbacks) test at the tail of context_switch with an unlikely(rq->balance_work), the fast path is not affected. Signed-off-by:
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Peter Zijlstra authored
The intent of balance_callback() has always been to delay executing balancing operations until the end of the current rq->lock section. This is because balance operations must often drop rq->lock, and that isn't safe in general. However, as noted by Scott, there were a few holes in that scheme; balance_callback() was called after rq->lock was dropped, which means another CPU can interleave and touch the callback list. Rework code to call the balance callbacks before dropping rq->lock where possible, and otherwise splice the balance list onto a local stack. This guarantees that the balance list must be empty when we take rq->lock. IOW, we'll only ever run our own balance callbacks. Reported-by:
Scott Wood <swood@redhat.com> Signed-off-by:
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Peter Zijlstra authored
Crashes in stop-machine are hard to connect to the calling code, add a little something to help with that. Signed-off-by:
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Peng Wang authored
As commit: 39f23ce0 ("sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list") does in unthrottle_cfs_rq(), throttle_cfs_rq() can also use the same pattern as dequeue_task_fair(). No functional changes. Signed-off-by:
Peng Wang <rocking@linux.alibaba.com> Signed-off-by:
Ingo Molnar <mingo@kernel.org> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Phil Auld <pauld@redhat.com> Cc: Ben Segall <bsegall@google.com> Link: https://lore.kernel.org/r/f11dd2e3ab35cc538e2eb57bf0c99b6eaffce127.1604973978.git.rocking@linux.alibaba.com
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- 29 Oct, 2020 14 commits
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Julia Lawall authored
In the case of a thread wakeup, wake_affine determines whether a core will be chosen for the thread on the socket where the thread ran previously or on the socket of the waker. This is done primarily by comparing the load of the core where th thread ran previously (prev) and the load of the waker (this). commit 11f10e54 ("sched/fair: Use load instead of runnable load in wakeup path") changed the load computation from the runnable load to the load average, where the latter includes the load of threads that have already blocked on the core. When a short-running daemon processes happens to run on prev, this change raised the situation that prev could appear to have a greater load than this, even when prev is actually idle. When prev and this are on the same socket, the idle prev is detected later, in select_idle_sibling. But if that does not hold, prev is completely ignored, causing the waking thread to move to the socket of the waker. In the case of N mostly active threads on N cores, this triggers other migrations and hurts performance. In contrast, before commit 11f10e54, the load on an idle core was 0, and in the case of a non-idle waker core, the effect of wake_affine was to select prev as the target for searching for a core for the waking thread. To avoid unnecessary migrations, extend wake_affine_idle to check whether the core where the thread previously ran is currently idle, and if so simply return that core as the target. [1] commit 11f10e54 ("sched/fair: Use load instead of runnable load in wakeup path") This particularly has an impact when using the ondemand power manager, where kworkers run every 0.004 seconds on all cores, increasing the likelihood that an idle core will be considered to have a load. The following numbers were obtained with the benchmarking tool hyperfine (https://github.com/sharkdp/hyperfine) on the NAS parallel benchmarks (https://www.nas.nasa.gov/publications/npb.html). The tests were run on an 80-core Intel(R) Xeon(R) CPU E7-8870 v4 @ 2.10GHz. Active (intel_pstate) and passive (intel_cpufreq) power management were used. Times are in seconds. All experiments use all 160 hardware threads. v5.9/intel-pstate v5.9+patch/intel-pstate bt.C.c 24.725724+-0.962340 23.349608+-1.607214 lu.C.x 29.105952+-4.804203 25.249052+-5.561617 sp.C.x 31.220696+-1.831335 30.227760+-2.429792 ua.C.x 26.606118+-1.767384 25.778367+-1.263850 v5.9/ondemand v5.9+patch/ondemand bt.C.c 25.330360+-1.028316 23.544036+-1.020189 lu.C.x 35.872659+-4.872090 23.719295+-3.883848 sp.C.x 32.141310+-2.289541 29.125363+-0.872300 ua.C.x 29.024597+-1.667049 25.728888+-1.539772 On the smaller data sets (A and B) and on the other NAS benchmarks there is no impact on performance. This also has a major impact on the splash2x.volrend benchmark of the parsec benchmark suite that goes from 1m25 without this patch to 0m45, in active (intel_pstate) mode. Fixes: 11f10e54 ("sched/fair: Use load instead of runnable load in wakeup path") Signed-off-by:
Julia Lawall <Julia.Lawall@inria.fr> Signed-off-by:
Mel Gorman <mgorman@suse.de> Link: https://lkml.kernel.org/r/1603372550-14680-1-git-send-email-Julia.Lawall@inria.fr
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Peter Zijlstra authored
Florian reported that all of kernel/sched/ is rebuild when CONFIG_BLK_DEV_INITRD is changed, which, while not a bug is unexpected. This is due to us including vmlinux.lds.h. Jakub explained that the problem is that we put the alignment requirement on the type instead of on a variable. Type alignment is a minimum, the compiler is free to pick any larger alignment for a specific instance of the type (eg. the variable). So force the type alignment on all individual variable definitions and remove the undesired dependency on vmlinux.lds.h. Fixes: 85c2ce91 ("sched, vmlinux.lds: Increase STRUCT_ALIGNMENT to 64 bytes for GCC-4.9") Reported-by:
Florian Fainelli <f.fainelli@gmail.com> Suggested-by:
Jakub Jelinek <jakub@redhat.com> Signed-off-by:
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Thomas Gleixner authored
do_sched_yield() invokes schedule() with interrupts disabled which is not allowed. This goes back to the pre git era to commit a6efb709 ("[PATCH] irqlock patch 2.5.27-H6") in the history tree. Reenable interrupts and remove the misleading comment which "explains" it. Fixes: 1da177e4 ("Linux-2.6.12-rc2") Signed-off-by:
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Mathieu Desnoyers authored
Document membarrier ordering scenarios in membarrier.c. Thanks to Alan Stern for refreshing my memory. Now that I have those in mind, it seems appropriate to serialize them to comments for posterity. Signed-off-by:
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by:
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Mathieu Desnoyers authored
Add comments and memory barrier to kthread_use_mm and kthread_unuse_mm to allow the effect of membarrier(2) to apply to kthreads accessing user-space memory as well. Given that no prior kthread use this guarantee and that it only affects kthreads, adding this guarantee does not affect user-space ABI. Refine the check in membarrier_global_expedited to exclude runqueues running the idle thread rather than all kthreads from the IPI cpumask. Now that membarrier_global_expedited can IPI kthreads, the scheduler also needs to update the runqueue's membarrier_state when entering lazy TLB state. Signed-off-by:
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Mathieu Desnoyers authored
exit_mm should issue memory barriers after user-space memory accesses, before clearing current->mm, to order user-space memory accesses performed prior to exit_mm before clearing tsk->mm, which has the effect of skipping the membarrier private expedited IPIs. exit_mm should also update the runqueue's membarrier_state so membarrier global expedited IPIs are not sent when they are not needed. The membarrier system call can be issued concurrently with do_exit if we have thread groups created with CLONE_VM but not CLONE_THREAD. Here is the scenario I have in mind: Two thread groups are created, A and B. Thread group B is created by issuing clone from group A with flag CLONE_VM set, but not CLONE_THREAD. Let's assume we have a single thread within each thread group (Thread A and Thread B). The AFAIU we can have: Userspace variables: int x = 0, y = 0; CPU 0 CPU 1 Thread A Thread B (in thread group A) (in thread group B) x = 1 barrier() y = 1 exit() exit_mm() current->mm = NULL; r1 = load y membarrier() skips CPU 0 (no IPI) because its current mm is NULL r2 = load x BUG_ON(r1 == 1 && r2 == 0) Signed-off-by: -
Peter Zijlstra authored
It is possible for find_new_ilb() to select the current CPU, however, this only happens from newidle balancing, in which case need_resched() will be true, and consequently nohz_csd_func() will not trigger the softirq. Exclude the current CPU from becoming an ILB target. Signed-off-by: -
Peter Zijlstra authored
Add CPUPRI_HIGHER above the RT99 priority to denote the CPU is in use by higher priority tasks (specifically deadline). XXX: we should probably drive PUSH-PULL from cpupri, that would automagically result in an RT-PUSH when DL sets cpupri to CPUPRI_HIGHER. Signed-off-by:
Dietmar Eggemann <dietmar.eggemann@arm.com>
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Peter Zijlstra authored
This makes the mapping continuous and frees up 100 for other usage. Prev mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 100 0 (CPUPRI_NORMAL) 1 98 98 1 ... 49 50 50 49 50 49 49 50 ... 99 0 0 99 New mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 99 0 (CPUPRI_NORMAL) 1 98 98 1 ... 49 50 50 49 50 49 49 50 ... 99 0 0 99 Signed-off-by: -
Dietmar Eggemann authored
pri_to_cpu[1] isn't used since cpupri_set(..., newpri) is never called with newpri = 99. The valid RT priorities RT1..RT99 (p->rt_priority = [1..99]) map into cpupri (idx of pri_to_cpu[]) = [2..100] Current mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 100 0 (CPUPRI_NORMAL) 1 98 98 2 ... 49 50 50 50 50 49 49 51 ... 99 0 0 100 So cpupri = 1 isn't used. Reduce the size of pri_to_cpu[] by 1 and adapt the cpupri implementation accordingly. This will save a useless for loop with an atomic_read in cpupri_find_fitness() calling __cpupri_find(). New mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 100 0 (CPUPRI_NORMAL) 1 98 98 1 ... 49 50 50 49 50 49 49 50 ... 99 0 0 99 Signed-off-by: -
Dietmar Eggemann authored
pri_to_cpu[CPUPRI_IDLE=0] isn't used since cpupri_set(..., newpri) is never called with newpri = MAX_PRIO (140). Current mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 140 0 (CPUPRI_IDLE) 100 1 (CPUPRI_NORMAL) 1 98 98 3 ... 49 50 50 51 50 49 49 52 ... 99 0 0 101 Even when cpupri was introduced with commit 6e0534f2 ("sched: use a 2-d bitmap for searching lowest-pri CPU") in v2.6.27, only (1) CPUPRI_INVALID (-1), (2) MAX_RT_PRIO (100), (3) an RT prio (RT1..RT99) were used as newprio in cpupri_set(..., newpri) -> convert_prio(newpri). MAX_RT_PRIO is used only in dec_rt_tasks() -> dec_rt_prio() -> dec_rt_prio_smp() -> cpupri_set() in case of !rt_rq->rt_nr_running. I.e. it stands for a non-rt task, including the IDLE task. Commit 57785df5 ("sched: Fix task priority bug") removed code in v2.6.33 which did set the priority of the IDLE task to MAX_PRIO. Although this happened after the introduction of cpupri, it didn't have an effect on the values used for cpupri_set(..., newpri). Remove CPUPRI_IDLE and adapt the cpupri implementation accordingly. This will save a useless for loop with an atomic_read in cpupri_find_fitness() calling __cpupri_find(). New mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 100 0 (CPUPRI_NORMAL) 1 98 98 2 ... 49 50 50 50 50 49 49 51 ... 99 0 0 100 Signed-off-by: -
Peng Liu authored
When change sched_rt_{runtime, period}_us, we validate that the new settings should at least accommodate the currently allocated -dl bandwidth: sched_rt_handler() --> sched_dl_bandwidth_validate() { new_bw = global_rt_runtime()/global_rt_period(); for_each_possible_cpu(cpu) { dl_b = dl_bw_of(cpu); if (new_bw < dl_b->total_bw) <------- ret = -EBUSY; } } But under CONFIG_SMP, dl_bw is per root domain , but not per CPU, dl_b->total_bw is the allocated bandwidth of the whole root domain. Instead, we should compare dl_b->total_bw against "cpus*new_bw", where 'cpus' is the number of CPUs of the root domain. Also, below annotation(in kernel/sched/sched.h) implied implementation only appeared in SCHED_DEADLINE v2[1], then deadline scheduler kept evolving till got merged(v9), but the annotation remains unchanged, meaningless and misleading, update it. * With respect to SMP, the bandwidth is given on a per-CPU basis, * meaning that: * - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU; * - dl_total_bw array contains, in the i-eth element, the currently * allocated bandwidth on the i-eth CPU. [1]: https://lore.kernel.org/lkml/1267385230.13676.101.camel@Palantir/ Fixes: 332ac17e ("sched/deadline: Add bandwidth management for SCHED_DEADLINE tasks") Signed-off-by:Peng Liu <iwtbavbm@gmail.com> Signed-off-by:
Juri Lelli <juri.lelli@redhat.com> Link: https://lkml.kernel.org/r/db6bbda316048cda7a1bbc9571defde193a8d67e.1602171061.git.iwtbavbm@gmail.com
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Peng Liu authored
Under CONFIG_SMP, dl_bw is per root domain, but not per CPU. When checking or updating dl_bw, currently iterating every CPU is overdoing, just need iterate each root domain once. Suggested-by:
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jun qian authored
When the sched_schedstat changes from 0 to 1, some sched se maybe already in the runqueue, the se->statistics.wait_start will be 0. So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start) wrong. We need to avoid this scenario. Signed-off-by:
jun qian <qianjun.kernel@gmail.com> Signed-off-by:
Yafang Shao <laoar.shao@gmail.com> Link: https://lkml.kernel.org/r/20201015064846.19809-1-qianjun.kernel@gmail.com
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