linux/kernel/sched/idle_task.c, branch v4.5

sched/fair: Remove empty idle enter and exit functions

2015-11-23T08:37:51Z

Commit cd126afe838d ("sched/fair: Remove rq's runnable avg") got rid of rq->avg and so there is no need to update it any more when entering or exiting idle. Remove the now empty functions idle_{enter|exit}_fair(). Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Yuyang Du Link: http://lkml.kernel.org/r/1445342681-17171-1-git-send-email-dietmar.eggemann@arm.com Signed-off-by: Ingo Molnar

sched: Make sched_class::set_cpus_allowed() unconditional

2015-08-12T10:06:09Z

Give every class a set_cpus_allowed() method, this enables some small optimization in the RT,DL implementation by avoiding a double cpumask_weight() call. Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dedekind1@gmail.com Cc: juri.lelli@arm.com Cc: mgorman@suse.de Cc: riel@redhat.com Cc: rostedt@goodmis.org Link: http://lkml.kernel.org/r/20150515154833.614517487@infradead.org Signed-off-by: Ingo Molnar

sched: Provide update_curr callbacks for stop/idle scheduling classes

2014-11-23T22:14:40Z

Chris bisected a NULL pointer deference in task_sched_runtime() to commit 6e998916dfe3 'sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency'. Chris observed crashes in atop or other /proc walking programs when he started fork bombs on his machine. He assumed that this is a new exit race, but that does not make any sense when looking at that commit. What's interesting is that, the commit provides update_curr callbacks for all scheduling classes except stop_task and idle_task. While nothing can ever hit that via the clock_nanosleep() and clock_gettime() interfaces, which have been the target of the commit in question, the author obviously forgot that there are other code paths which invoke task_sched_runtime() do_task_stat(() thread_group_cputime_adjusted() thread_group_cputime() task_cputime() task_sched_runtime() if (task_current(rq, p) && task_on_rq_queued(p)) { update_rq_clock(rq); up->sched_class->update_curr(rq); } If the stats are read for a stomp machine task, aka 'migration/N' and that task is current on its cpu, this will happily call the NULL pointer of stop_task->update_curr. Ooops. Chris observation that this happens faster when he runs the fork bomb makes sense as the fork bomb will kick migration threads more often so the probability to hit the issue will increase. Add the missing update_curr callbacks to the scheduler classes stop_task and idle_task. While idle tasks cannot be monitored via /proc we have other means to hit the idle case. Fixes: 6e998916dfe3 'sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency' Reported-by: Chris Mason Reported-and-tested-by: Borislav Petkov Signed-off-by: Thomas Gleixner Cc: Ingo Molnar Cc: Stanislaw Gruszka Cc: Peter Zijlstra Signed-off-by: Linus Torvalds

sched: Transform resched_task() into resched_curr()

2014-07-16T11:38:19Z

We always use resched_task() with rq->curr argument. It's not possible to reschedule any task but rq's current. The patch introduces resched_curr(struct rq *) to replace all of the repeating patterns. The main aim is cleanup, but there is a little size profit too: (before) $ size kernel/sched/built-in.o text data bss dec hex filename 155274 16445 7042 178761 2ba49 kernel/sched/built-in.o $ size vmlinux text data bss dec hex filename 7411490 1178376 991232 9581098 92322a vmlinux (after) $ size kernel/sched/built-in.o text data bss dec hex filename 155130 16445 7042 178617 2b9b9 kernel/sched/built-in.o $ size vmlinux text data bss dec hex filename 7411362 1178376 991232 9580970 9231aa vmlinux I was choosing between resched_curr() and resched_rq(), and the first name looks better for me. A little lie in Documentation/trace/ftrace.txt. I have not actually collected the tracing again. With a hope the patch won't make execution times much worse :) Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Cc: Randy Dunlap Cc: Steven Rostedt Link: http://lkml.kernel.org/r/20140628200219.1778.18735.stgit@localhost Signed-off-by: Ingo Molnar

sched/fair: Push down check for high priority class task into idle_balance()

2014-03-11T11:05:37Z

We close idle_exit_fair() bracket in case of we've pulled something or we've received task of high priority class. Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra Cc: Vincent Guittot Link: http://lkml.kernel.org/r/1394098315.19290.10.camel@tkhai Signed-off-by: Ingo Molnar

sched: Remove some #ifdeffery

2014-02-21T20:43:18Z

Remove a few gratuitous #ifdefs in pick_next_task*(). Cc: Ingo Molnar Cc: Steven Rostedt Cc: Juri Lelli Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-nnzddp5c4fijyzzxxrwlxghf@git.kernel.org Signed-off-by: Thomas Gleixner

sched: Fix hotplug task migration

2014-02-21T20:43:18Z

Dan Carpenter reported: > kernel/sched/rt.c:1347 pick_next_task_rt() warn: variable dereferenced before check 'prev' (see line 1338) > kernel/sched/deadline.c:1011 pick_next_task_dl() warn: variable dereferenced before check 'prev' (see line 1005) Kirill also spotted that migrate_tasks() will have an instant NULL deref because pick_next_task() will immediately deref prev. Instead of fixing all the corner cases because migrate_tasks() can pass in a NULL prev task in the unlikely case of hot-un-plug, provide a fake task such that we can remove all the NULL checks from the far more common paths. A further problem; not previously spotted; is that because we pushed pre_schedule() and idle_balance() into pick_next_task() we now need to avoid those getting called and pulling more tasks on our dying CPU. We avoid pull_{dl,rt}_task() by setting fake_task.prio to MAX_PRIO+1. We also note that since we call pick_next_task() exactly the amount of times we have runnable tasks present, we should never land in idle_balance(). Fixes: 38033c37faab ("sched: Push down pre_schedule() and idle_balance()") Cc: Juri Lelli Cc: Ingo Molnar Cc: Steven Rostedt Reported-by: Kirill Tkhai Reported-by: Dan Carpenter Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140212094930.GB3545@laptop.programming.kicks-ass.net Signed-off-by: Thomas Gleixner

sched: Push down pre_schedule() and idle_balance()

2014-02-11T08:58:10Z

This patch both merged idle_balance() and pre_schedule() and pushes both of them into pick_next_task(). Conceptually pre_schedule() and idle_balance() are rather similar, both are used to pull more work onto the current CPU. We cannot however first move idle_balance() into pre_schedule_fair() since there is no guarantee the last runnable task is a fair task, and thus we would miss newidle balances. Similarly, the dl and rt pre_schedule calls must be ran before idle_balance() since their respective tasks have higher priority and it would not do to delay their execution searching for less important tasks first. However, by noticing that pick_next_tasks() already traverses the sched_class hierarchy in the right order, we can get the right behaviour and do away with both calls. We must however change the special case optimization to also require that prev is of sched_class_fair, otherwise we can miss doing a dl or rt pull where we needed one. Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/n/tip-a8k6vvaebtn64nie345kx1je@git.kernel.org Signed-off-by: Ingo Molnar

sched: Clean up idle task SMP logic

2014-02-10T15:17:22Z

The idle post_schedule flag is just a vile waste of time, furthermore it appears unneeded, move the idle_enter_fair() call into pick_next_task_idle(). Signed-off-by: Peter Zijlstra Cc: Daniel Lezcano Cc: Vincent Guittot Cc: alex.shi@linaro.org Cc: mingo@kernel.org Cc: Steven Rostedt Link: http://lkml.kernel.org/n/tip-aljykihtxJt3mkokxi0qZurb@git.kernel.org Signed-off-by: Ingo Molnar

sched: Push put_prev_task() into pick_next_task()

2014-02-10T15:17:13Z

In order to avoid having to do put/set on a whole cgroup hierarchy when we context switch, push the put into pick_next_task() so that both operations are in the same function. Further changes then allow us to possibly optimize away redundant work. Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1328936700.2476.17.camel@laptop Signed-off-by: Ingo Molnar