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  1. 25 1月, 2013 2 次提交
    • Y
      sched/rt: Avoid updating RT entry timeout twice within one tick period · 57d2aa00
      由 Ying Xue 提交于 
      The issue below was found in 2.6.34-rt rather than mainline rt
kernel, but the issue still exists upstream as well.

So please let me describe how it was noticed on 2.6.34-rt:

On this version, each softirq has its own thread, it means there
is at least one RT FIFO task per cpu. The priority of these
tasks is set to 49 by default. If user launches an RT FIFO task
with priority lower than 49 of softirq RT tasks, it's possible
there are two RT FIFO tasks enqueued one cpu runqueue at one
moment. By current strategy of balancing RT tasks, when it comes
to RT tasks, we really need to put them off to a CPU that they
can run on as soon as possible. Even if it means a bit of cache
line flushing, we want RT tasks to be run with the least latency.

When the user RT FIFO task which just launched before is
running, the sched timer tick of the current cpu happens. In this
tick period, the timeout value of the user RT task will be
updated once. Subsequently, we try to wake up one softirq RT
task on its local cpu. As the priority of current user RT task
is lower than the softirq RT task, the current task will be
preempted by the higher priority softirq RT task. Before
preemption, we check to see if current can readily move to a
different cpu. If so, we will reschedule to allow the RT push logic
to try to move current somewhere else. Whenever the woken
softirq RT task runs, it first tries to migrate the user FIFO RT
task over to a cpu that is running a task of lesser priority. If
migration is done, it will send a reschedule request to the found
cpu by IPI interrupt. Once the target cpu responds the IPI
interrupt, it will pick the migrated user RT task to preempt its
current task. When the user RT task is running on the new cpu,
the sched timer tick of the cpu fires. So it will tick the user
RT task again. This also means the RT task timeout value will be
updated again. As the migration may be done in one tick period,
it means the user RT task timeout value will be updated twice
within one tick.

If we set a limit on the amount of cpu time for the user RT task
by setrlimit(RLIMIT_RTTIME), the SIGXCPU signal should be posted
upon reaching the soft limit.

But exactly when the SIGXCPU signal should be sent depends on the
RT task timeout value. In fact the timeout mechanism of sending
the SIGXCPU signal assumes the RT task timeout is increased once
every tick.

However, currently the timeout value may be added twice per
tick. So it results in the SIGXCPU signal being sent earlier
than expected.

To solve this issue, we prevent the timeout value from increasing
twice within one tick time by remembering the jiffies value of
last updating the timeout. As long as the RT task's jiffies is
different with the global jiffies value, we allow its timeout to
be updated.
Signed-off-by: NYing Xue <ying.xue@windriver.com>
Signed-off-by: NFan Du <fan.du@windriver.com>
Reviewed-by: NYong Zhang <yong.zhang0@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1342508623-2887-1-git-send-email-ying.xue@windriver.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      57d2aa00
    • K
      sched/rt: Add reschedule check to switched_from_rt() · 1158ddb5
      由 Kirill Tkhai 提交于 
      Reschedule rq->curr if the first RT task has just been
pulled to the rq.
Signed-off-by: NKirill V Tkhai <tkhai@yandex.ru>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tkhai Kirill <tkhai@yandex.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/118761353614535@web28f.yandex.ruSigned-off-by: NIngo Molnar <mingo@kernel.org>
      1158ddb5
  3. 13 9月, 2012 1 次提交
  5. 04 9月, 2012 1 次提交
  7. 14 8月, 2012 1 次提交
  9. 06 6月, 2012 1 次提交
  11. 30 5月, 2012 2 次提交
  13. 13 4月, 2012 1 次提交
  15. 27 3月, 2012 1 次提交
  17. 13 3月, 2012 1 次提交
  19. 01 3月, 2012 2 次提交
  21. 22 2月, 2012 1 次提交
  23. 27 1月, 2012 1 次提交
    • C
      sched/rt: Fix task stack corruption under __ARCH_WANT_INTERRUPTS_ON_CTXSW · cb297a3e
      由 Chanho Min 提交于 
      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: NChanho Min <chanho.min@lge.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/CAOAMb1BHA=5fm7KTewYyke6u-8DP0iUuJMpgQw54vNeXFsGpoQ@mail.gmail.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      cb297a3e
  25. 06 12月, 2011 2 次提交
    • S
      sched/rt: Code cleanup, remove a redundant function call · 5b680fd6
      由 Shan Hai 提交于 
      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: NShan Hai <haishan.bai@gmail.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1322535836-13590-2-git-send-email-haishan.bai@gmail.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      5b680fd6
    • M
      sched: Use rt.nr_cpus_allowed to recover select_task_rq() cycles · 76854c7e
      由 Mike Galbraith 提交于 
      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: NMike Galbraith <efault@gmx.de>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1321971504.6855.15.camel@marge.simson.netSigned-off-by: NIngo Molnar <mingo@elte.hu>
      76854c7e
  27. 17 11月, 2011 2 次提交
  29. 16 11月, 2011 1 次提交
  31. 14 11月, 2011 1 次提交
  33. 06 10月, 2011 3 次提交
  35. 18 9月, 2011 1 次提交
  37. 14 8月, 2011 6 次提交
  39. 01 7月, 2011 1 次提交
  41. 15 6月, 2011 2 次提交
  43. 28 5月, 2011 1 次提交
  45. 16 5月, 2011 2 次提交
  47. 14 4月, 2011 2 次提交
  49. 31 3月, 2011 1 次提交