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Avoid extra work by continuing on to the next rt_rq if the highest
prio task in current rt_rq is the same priority as our candidate
task.
More detailed explanation: if next is not NULL, then we have found a
candidate task, and its priority is next->prio. Now we are looking
for an even higher priority task in the other rt_rq's. idx is the
highest priority in the current candidate rt_rq. In the current 3.3
code, if idx is equal to next->prio, we would start scanning the tasks
in that rt_rq and replace the current candidate task with a task from
that rt_rq. But the new task would only have a priority that is equal
to our previous candidate task, so we have not advanced our goal of
finding a higher prio task. So we should avoid the extra work by
continuing on to the next rt_rq if idx is equal to next->prio.
Signed-off-by: Michael J Wang <mjwang@broadcom.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/2EF88150C0EF2C43A218742ED384C1BC0FC83D6B@IRVEXCHMB08.corp.ad.broadcom.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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There's a few awkward printk()s inside of scheduler guts that people
prefer to keep but really are rather deadlock prone. Fudge around it
by storing the text in a per-cpu buffer and poll it using the existing
printk_tick() handler.
This will drop output when its more frequent than once a tick, however
only the affinity thing could possible go that fast and for that just
one should suffice to notify the admin he's done something silly..
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-wua3lmkt3dg8nfts66o6brne@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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When a runqueue has rt_runtime_us = 0 then the only way it can
accumulate rt_time is via PI boosting. That causes the runqueue
to be throttled and replenishing does not change anything due to
rt_runtime_us = 0. So avoid that situation by clearing rt_time and
skip the throttling alltogether.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
[ Changelog ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-7x70cypsotjb4jvcor3edctk@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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When a runqueue is throttled we cannot disable the period timer
because that timer is the only way to undo the throttling.
We got stale throttling entries when a rq was throttled and then the
global sysctl was disabled, which stopped the timer.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
[ Added changelog ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-nuj34q52p6ro7szapuz84i0v@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Current the initial SCHED_RR timeslice of init_task is HZ, which means
1s, and is not same as the default SCHED_RR timeslice DEF_TIMESLICE.
Change that initial timeslice to the DEF_TIMESLICE.
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
[ s/DEF_TIMESLICE/RR_TIMESLICE/g ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4F3C9995.3010800@ct.jp.nec.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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This issue happens under the following conditions:
1. preemption is off
2. __ARCH_WANT_INTERRUPTS_ON_CTXSW is defined
3. RT scheduling class
4. SMP system
Sequence is as follows:
1.suppose current task is A. start schedule()
2.task A is enqueued pushable task at the entry of schedule()
__schedule
prev = rq->curr;
...
put_prev_task
put_prev_task_rt
enqueue_pushable_task
4.pick the task B as next task.
next = pick_next_task(rq);
3.rq->curr set to task B and context_switch is started.
rq->curr = next;
4.At the entry of context_swtich, release this cpu's rq->lock.
context_switch
prepare_task_switch
prepare_lock_switch
raw_spin_unlock_irq(&rq->lock);
5.Shortly after rq->lock is released, interrupt is occurred and start IRQ context
6.try_to_wake_up() which called by ISR acquires rq->lock
try_to_wake_up
ttwu_remote
rq = __task_rq_lock(p)
ttwu_do_wakeup(rq, p, wake_flags);
task_woken_rt
7.push_rt_task picks the task A which is enqueued before.
task_woken_rt
push_rt_tasks(rq)
next_task = pick_next_pushable_task(rq)
8.At find_lock_lowest_rq(), If double_lock_balance() returns 0,
lowest_rq can be the remote rq.
(But,If preemption is on, double_lock_balance always return 1 and it
does't happen.)
push_rt_task
find_lock_lowest_rq
if (double_lock_balance(rq, lowest_rq))..
9.find_lock_lowest_rq return the available rq. task A is migrated to
the remote cpu/rq.
push_rt_task
...
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, lowest_rq->cpu);
activate_task(lowest_rq, next_task, 0);
10. But, task A is on irq context at this cpu.
So, task A is scheduled by two cpus at the same time until restore from IRQ.
Task A's stack is corrupted.
To fix it, don't migrate an RT task if it's still running.
Signed-off-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/CAOAMb1BHA=5fm7KTewYyke6u-8DP0iUuJMpgQw54vNeXFsGpoQ@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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The second call to sched_rt_period() is redundant, because the value of the
rt_runtime was already read and it was protected by the ->rt_runtime_lock.
Signed-off-by: Shan Hai <haishan.bai@gmail.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1322535836-13590-2-git-send-email-haishan.bai@gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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rt.nr_cpus_allowed is always available, use it to bail from select_task_rq()
when only one cpu can be used, and saves some cycles for pinned tasks.
See the line marked with '*' below:
# taskset -c 3 pipe-test
PerfTop: 997 irqs/sec kernel:89.5% exact: 0.0% [1000Hz cycles], (all, CPU: 3)
------------------------------------------------------------------------------------------------
Virgin Patched
samples pcnt function samples pcnt function
_______ _____ ___________________________ _______ _____ ___________________________
2880.00 10.2% __schedule 3136.00 11.3% __schedule
1634.00 5.8% pipe_read 1615.00 5.8% pipe_read
1458.00 5.2% system_call 1534.00 5.5% system_call
1382.00 4.9% _raw_spin_lock_irqsave 1412.00 5.1% _raw_spin_lock_irqsave
1202.00 4.3% pipe_write 1255.00 4.5% copy_user_generic_string
1164.00 4.1% copy_user_generic_string 1241.00 4.5% __switch_to
1097.00 3.9% __switch_to 929.00 3.3% mutex_lock
872.00 3.1% mutex_lock 846.00 3.0% mutex_unlock
687.00 2.4% mutex_unlock 804.00 2.9% pipe_write
682.00 2.4% native_sched_clock 713.00 2.6% native_sched_clock
643.00 2.3% system_call_after_swapgs 653.00 2.3% _raw_spin_unlock_irqrestore
617.00 2.2% sched_clock_local 633.00 2.3% fsnotify
612.00 2.2% fsnotify 605.00 2.2% sched_clock_local
596.00 2.1% _raw_spin_unlock_irqrestore 593.00 2.1% system_call_after_swapgs
542.00 1.9% sysret_check 559.00 2.0% sysret_check
467.00 1.7% fget_light 472.00 1.7% fget_light
462.00 1.6% finish_task_switch 461.00 1.7% finish_task_switch
437.00 1.5% vfs_write 442.00 1.6% vfs_write
431.00 1.5% do_sync_write 428.00 1.5% do_sync_write
* 413.00 1.5% select_task_rq_fair 404.00 1.5% _raw_spin_lock_irq
386.00 1.4% update_curr 402.00 1.4% update_curr
385.00 1.4% rw_verify_area 389.00 1.4% do_sync_read
377.00 1.3% _raw_spin_lock_irq 378.00 1.4% vfs_read
369.00 1.3% do_sync_read 340.00 1.2% pipe_iov_copy_from_user
360.00 1.3% vfs_read 316.00 1.1% __wake_up_sync_key
342.00 1.2% hrtick_start_fair 313.00 1.1% __wake_up_common
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1321971504.6855.15.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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There's too many sched*.[ch] files in kernel/, give them their own
directory.
(No code changed, other than Makefile glue added.)
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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