linux/kernel/sched/rt.c, branch v5.15

sched/rt: Fix RT utilization tracking during policy change

2021-06-22T14:41:59Z

RT keeps track of the utilization on a per-rq basis with the structure avg_rt. This utilization is updated during task_tick_rt(), put_prev_task_rt() and set_next_task_rt(). However, when the current running task changes its policy, set_next_task_rt() which would usually take care of updating the utilization when the rq starts running RT tasks, will not see a such change, leaving the avg_rt structure outdated. When that very same task will be dequeued later, put_prev_task_rt() will then update the utilization, based on a wrong last_update_time, leading to a huge spike in the RT utilization signal. The signal would eventually recover from this issue after few ms. Even if no RT tasks are run, avg_rt is also updated in __update_blocked_others(). But as the CPU capacity depends partly on the avg_rt, this issue has nonetheless a significant impact on the scheduler. Fix this issue by ensuring a load update when a running task changes its policy to RT. Fixes: 371bf427 ("sched/rt: Add rt_rq utilization tracking") Signed-off-by: Vincent Donnefort Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/1624271872-211872-2-git-send-email-vincent.donnefort@arm.com

sched: Introduce sched_class::pick_task()

2021-05-12T09:43:28Z

Because sched_class::pick_next_task() also implies sched_class::set_next_task() (and possibly put_prev_task() and newidle_balance) it is not state invariant. This makes it unsuitable for remote task selection. Signed-off-by: Peter Zijlstra (Intel) [Vineeth: folded fixes] Signed-off-by: Vineeth Remanan Pillai Signed-off-by: Peter Zijlstra (Intel) Tested-by: Don Hiatt Tested-by: Hongyu Ning Tested-by: Vincent Guittot Link: https://lkml.kernel.org/r/20210422123308.437092775@infradead.org

sched: Wrap rq::lock access

2021-05-12T09:43:26Z

In preparation of playing games with rq->lock, abstract the thing using an accessor. Signed-off-by: Peter Zijlstra (Intel) Tested-by: Don Hiatt Tested-by: Hongyu Ning Tested-by: Vincent Guittot Link: https://lkml.kernel.org/r/20210422123308.136465446@infradead.org

sched: Fix various typos

2021-03-21T23:11:52Z

Fix ~42 single-word typos in scheduler code comments. We have accumulated a few fun ones over the years. :-) Signed-off-by: Ingo Molnar Cc: Peter Zijlstra Cc: Mike Galbraith Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: linux-kernel@vger.kernel.org

sched: Use task_current() instead of 'rq->curr == p'

2021-01-14T10:20:11Z

Use the task_current() function where appropriate. No functional change. Signed-off-by: Hui Su Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (VMware) Link: https://lkml.kernel.org/r/20201030173223.GA52339@rlk

sched: Remove select_task_rq()'s sd_flag parameter

2020-11-10T17:39:06Z

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: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201102184514.2733-3-valentin.schneider@arm.com

Merge branch 'sched/migrate-disable'

2020-11-10T17:39:04Z

sched: Fix migrate_disable() vs rt/dl balancing

2020-11-10T17:39:01Z

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: Peter Zijlstra (Intel) Reviewed-by: Daniel Bristot de Oliveira Link: https://lkml.kernel.org/r/20201023102347.499155098@infradead.org

sched,rt: Use the full cpumask for balancing

2020-11-10T17:39:00Z

We want migrate_disable() tasks to get PULLs in order for them to PUSH away the higher priority task. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Daniel Bristot de Oliveira Link: https://lkml.kernel.org/r/20201023102347.310519774@infradead.org

sched,rt: Use cpumask_any*_distribute()

2020-11-10T17:39:00Z

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: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Daniel Bristot de Oliveira Link: https://lkml.kernel.org/r/20201023102347.190759694@infradead.org