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  1. 21 9月, 2009 1 次提交
  3. 15 9月, 2009 3 次提交
  5. 04 9月, 2009 1 次提交
  7. 02 8月, 2009 4 次提交
    • I
      sched: Fix cpupri build on !CONFIG_SMP · bcf08df3
      由 Ingo Molnar 提交于 
      This build bug:

 In file included from kernel/sched.c:1765:
 kernel/sched_rt.c: In function ‘has_pushable_tasks’:
 kernel/sched_rt.c:1069: error: ‘struct rt_rq’ has no member named ‘pushable_tasks’
 kernel/sched_rt.c: In function ‘pick_next_task_rt’:
 kernel/sched_rt.c:1084: error: ‘struct rq’ has no member named ‘post_schedule’

Triggers because both pushable_tasks and post_schedule are
SMP-only fields.

Move pushable_tasks() to the SMP section and #ifdef the post_schedule use.

Cc: Gregory Haskins <ghaskins@novell.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090729150422.17691.55590.stgit@dev.haskins.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      bcf08df3
    • P
      sched: Add debug check to task_of() · 8f48894f
      由 Peter Zijlstra 提交于 
      A frequent mistake appears to be to call task_of() on a
scheduler entity that is not actually a task, which can result
in a wild pointer.

Add a check to catch these mistakes.
Suggested-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      8f48894f
    • G
      sched: Fully integrate cpus_active_map and root-domain code · 00aec93d
      由 Gregory Haskins 提交于 
      Reflect "active" cpus in the rq->rd->online field, instead of
the online_map.

The motivation is that things that use the root-domain code
(such as cpupri) only care about cpus classified as "active"
anyway. By synchronizing the root-domain state with the active
map, we allow several optimizations.

For instance, we can remove an extra cpumask_and from the
scheduler hotpath by utilizing rq->rd->online (since it is now
a cached version of cpu_active_map & rq->rd->span).
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NMax Krasnyansky <maxk@qualcomm.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090730145723.25226.24493.stgit@dev.haskins.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      00aec93d
    • G
      sched: Enhance the pre/post scheduling logic · 3f029d3c
      由 Gregory Haskins 提交于 
      We currently have an explicit "needs_post" vtable method which
returns a stack variable for whether we should later run
post-schedule.  This leads to an awkward exchange of the
variable as it bubbles back up out of the context switch. Peter
Zijlstra observed that this information could be stored in the
run-queue itself instead of handled on the stack.

Therefore, we revert to the method of having context_switch
return void, and update an internal rq->post_schedule variable
when we require further processing.

In addition, we fix a race condition where we try to access
current->sched_class without holding the rq->lock.  This is
technically racy, as the sched-class could change out from
under us.  Instead, we reference the per-rq post_schedule
variable with the runqueue unlocked, but with preemption
disabled to see if we need to reacquire the rq->lock.

Finally, we clean the code up slightly by removing the #ifdef
CONFIG_SMP conditionals from the schedule() call, and implement
some inline helper functions instead.

This patch passes checkpatch, and rt-migrate.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090729150422.17691.55590.stgit@dev.haskins.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      3f029d3c
  9. 10 7月, 2009 1 次提交
  11. 09 6月, 2009 1 次提交
  13. 01 4月, 2009 1 次提交
  15. 01 2月, 2009 1 次提交
  17. 16 1月, 2009 1 次提交
    • P
      sched: make plist a library facility · ceacc2c1
      由 Peter Zijlstra 提交于 
      Ingo Molnar wrote:

> here's a new build failure with tip/sched/rt:
>
>   LD      .tmp_vmlinux1
> kernel/built-in.o: In function `set_curr_task_rt':
> sched.c:(.text+0x3675): undefined reference to `plist_del'
> kernel/built-in.o: In function `pick_next_task_rt':
> sched.c:(.text+0x37ce): undefined reference to `plist_del'
> kernel/built-in.o: In function `enqueue_pushable_task':
> sched.c:(.text+0x381c): undefined reference to `plist_del'

Eliminate the plist library kconfig and make it available
unconditionally.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      ceacc2c1
  19. 14 1月, 2009 2 次提交
  21. 12 1月, 2009 1 次提交
  23. 04 1月, 2009 1 次提交
    • M
      sched: put back some stack hog changes that were undone in kernel/sched.c · 6ca09dfc
      由 Mike Travis 提交于 
      Impact: prevents panic from stack overflow on numa-capable machines.

Some of the "removal of stack hogs" changes in kernel/sched.c by using
node_to_cpumask_ptr were undone by the early cpumask API updates, and
causes a panic due to stack overflow.  This patch undoes those changes
by using cpumask_of_node() which returns a 'const struct cpumask *'.

In addition, cpu_coregoup_map is replaced with cpu_coregroup_mask further
reducing stack usage.  (Both of these updates removed 9 FIXME's!)

Also:
   Pick up some remaining changes from the old 'cpumask_t' functions to
   the new 'struct cpumask *' functions.

   Optimize memory traffic by allocating each percpu local_cpu_mask on the
   same node as the referring cpu.
Signed-off-by: NMike Travis <travis@sgi.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      6ca09dfc
  25. 29 12月, 2008 8 次提交
    • G
      RT: fix push_rt_task() to handle dequeue_pushable properly · 1563513d
      由 Gregory Haskins 提交于 
      A panic was discovered by Chirag Jog where a BUG_ON sanity check
in the new "pushable_task" logic would trigger a panic under
certain circumstances:

http://lkml.org/lkml/2008/9/25/189

Gilles Carry discovered that the root cause was attributed to the
pushable_tasks list getting corrupted in the push_rt_task logic.
This was the result of a dropped rq lock in double_lock_balance
allowing a task in the process of being pushed to potentially migrate
away, and thus corrupt the pushable_tasks() list.

I traced back the problem as introduced by the pushable_tasks patch
that went in recently.   There is a "retry" path in push_rt_task()
that actually had a compound conditional to decide whether to
retry or exit.  I missed the meaning behind the rationale for the
virtual "if(!task) goto out;" portion of the compound statement and
thus did not handle it properly.  The new pushable_tasks logic
actually creates three distinct conditions:

1) an untouched and unpushable task should be dequeued
2) a migrated task where more pushable tasks remain should be retried
3) a migrated task where no more pushable tasks exist should exit

The original logic mushed (1) and (3) together, resulting in the
system dequeuing a migrated task (against an unlocked foreign run-queue
nonetheless).

To fix this, we get rid of the notion of "paranoid" and we support the
three unique conditions properly.  The paranoid feature is no longer
relevant with the new pushable logic (since pushable naturally limits
the loop) anyway, so lets just remove it.
Reported-By: NChirag Jog <chirag@linux.vnet.ibm.com>
Found-by: NGilles Carry <gilles.carry@bull.net>
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      1563513d
    • G
      sched: create "pushable_tasks" list to limit pushing to one attempt · 917b627d
      由 Gregory Haskins 提交于 
      The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis).  When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted.  This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.

When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state.  Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over.  The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.

However, the current implementation suffers from a limitation in the
push logic.  Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc).  Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue.  This causes two problems:

1) We can have the same tasks analyzed over and over again during each
   push, which extends out the fast path in the scheduler for no
   gain.  Consider a RQ that has dozens of tasks that are bound to a
   core.  Each one of those tasks will be encountered and skipped
   for each push operation while they are queued.

2) There may be lower-priority tasks under the unpushable task that
   could have been successfully pushed, but will never be considered
   until either the unpushable task is cleared, or a pull operation
   succeeds.  The net result is a potential latency source for mid
   priority tasks.

This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks".  A task is added to the list
each time a task is activated or preempted.  It is removed from the
list any time it is deactivated, made current, or fails to push.

This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper.  This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks.  Now every task will have a push attempted (when
appropriate).

This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.

[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
Acked-by: NSteven Rostedt <srostedt@redhat.com>
      917b627d
    • G
      sched: add sched_class->needs_post_schedule() member · 967fc046
      由 Gregory Haskins 提交于 
      We currently run class->post_schedule() outside of the rq->lock, which
means that we need to test for the need to post_schedule outside of
the lock to avoid a forced reacquistion.  This is currently not a problem
as we only look at rq->rt.overloaded.  However, we want to enhance this
going forward to look at more state to reduce the need to post_schedule to
a bare minimum set.  Therefore, we introduce a new member-func called
needs_post_schedule() which tests for the post_schedule condtion without
actually performing the work.  Therefore it is safe to call this
function before the rq->lock is released, because we are guaranteed not
to drop the lock at an intermediate point (such as what post_schedule()
may do).

We will use this later in the series

[ rostedt: removed paranoid BUG_ON ]
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      967fc046
    • G
      sched: only try to push a task on wakeup if it is migratable · 777c2f38
      由 Gregory Haskins 提交于 
      There is no sense in wasting time trying to push a task away that
cannot move anywhere else.  We gain no benefit from trying to push
other tasks at this point, so if the task being woken up is non
migratable, just skip the whole operation.  This reduces overhead
in the wakeup path for certain tasks.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      777c2f38
    • G
      sched: use highest_prio.next to optimize pull operations · 74ab8e4f
      由 Gregory Haskins 提交于 
      We currently take the rq->lock for every cpu in an overload state during
pull_rt_tasks().  However, we now have enough information via the
highest_prio.[curr|next] fields to determine if there is any tasks of
interest to warrant the overhead of the rq->lock, before we actually take
it.  So we use this information to reduce lock contention during the
pull for the case where the source-rq doesnt have tasks that preempt
the current task.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      74ab8e4f
    • G
      sched: use highest_prio.curr for pull threshold · a8728944
      由 Gregory Haskins 提交于 
      highest_prio.curr is actually a more accurate way to keep track of
the pull_rt_task() threshold since it is always up to date, even
if the "next" task migrates during double_lock.  Therefore, stop
looking at the "next" task object and simply use the highest_prio.curr.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      a8728944
    • G
      sched: track the next-highest priority on each runqueue · e864c499
      由 Gregory Haskins 提交于 
      We will use this later in the series to reduce the amount of rq-lock
contention during a pull operation
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      e864c499
    • G
      sched: cleanup inc/dec_rt_tasks · 4d984277
      由 Gregory Haskins 提交于 
      Move some common definitions up to the function prologe to simplify the
body logic.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
      4d984277
  27. 17 12月, 2008 1 次提交
  29. 29 11月, 2008 1 次提交
    • A
      sched: move double_unlock_balance() higher · 70574a99
      由 Alexey Dobriyan 提交于 
      Move double_lock_balance()/double_unlock_balance() higher to fix the following
with gcc-3.4.6:

   CC      kernel/sched.o
 In file included from kernel/sched.c:1605:
 kernel/sched_rt.c: In function `find_lock_lowest_rq':
 kernel/sched_rt.c:914: sorry, unimplemented: inlining failed in call to 'double_unlock_balance': function body not available
 kernel/sched_rt.c:1077: sorry, unimplemented: called from here
 make[2]: *** [kernel/sched.o] Error 1
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      70574a99
  31. 26 11月, 2008 1 次提交
  33. 25 11月, 2008 5 次提交
  35. 07 11月, 2008 1 次提交
    • S
      sched, lockdep: inline double_unlock_balance() · cf7f8690
      由 Sripathi Kodi 提交于 
      We have a test case which measures the variation in the amount of time
needed to perform a fixed amount of work on the preempt_rt kernel. We
started seeing deterioration in it's performance recently. The test
should never take more than 10 microseconds, but we started 5-10%
failure rate.

Using elimination method, we traced the problem to commit
1b12bbc7 (lockdep: re-annotate
scheduler runqueues).

When LOCKDEP is disabled, this patch only adds an additional function
call to double_unlock_balance(). Hence I inlined double_unlock_balance()
and the problem went away. Here is a patch to make this change.
Signed-off-by: NSripathi Kodi <sripathik@in.ibm.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      cf7f8690
  37. 03 11月, 2008 1 次提交
    • D
      sched/rt: small optimization to update_curr_rt() · e113a745
      由 Dimitri Sivanich 提交于 
      Impact: micro-optimization to SCHED_FIFO/RR scheduling

A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
before taking the rt_runtime_lock?

Peter Zijlstra observes:

> Yes, I think its ok to do so.
>
> Like pointed out in the other thread, there are two races:
>
>  - sched_rt_runtime() going to RUNTIME_INF, and that will be handled
>    properly by sched_rt_runtime_exceeded()
>
>  - sched_rt_runtime() going to !RUNTIME_INF, and here we can miss an
>    accounting cycle, but I don't think that is something to worry too
>    much about.
Signed-off-by: NDimitri Sivanich <sivanich@sgi.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

--

 kernel/sched_rt.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
      e113a745
  39. 22 10月, 2008 1 次提交
  41. 04 10月, 2008 1 次提交
    • D
      sched_rt.c: resch needed in rt_rq_enqueue() for the root rt_rq · f6121f4f
      由 Dario Faggioli 提交于 
      While working on the new version of the code for SCHED_SPORADIC I
noticed something strange in the present throttling mechanism. More
specifically in the throttling timer handler in sched_rt.c
(do_sched_rt_period_timer()) and in rt_rq_enqueue().

The problem is that, when unthrottling a runqueue, rt_rq_enqueue() only
asks for rescheduling if the runqueue has a sched_entity associated to
it (i.e., rt_rq->rt_se != NULL).
Now, if the runqueue is the root rq (which has a rt_se = NULL)
rescheduling does not take place, and it is delayed to some undefined
instant in the future.

This imply some random bandwidth usage by the RT tasks under throttling.
For instance, setting rt_runtime_us/rt_period_us = 950ms/1000ms an RT
task will get less than 95%. In our tests we got something varying
between 70% to 95%.
Using smaller time values, e.g., 95ms/100ms, things are even worse, and
I can see values also going down to 20-25%!!

The tests we performed are simply running 'yes' as a SCHED_FIFO task,
and checking the CPU usage with top, but we can investigate thoroughly
if you think it is needed.

Things go much better, for us, with the attached patch... Don't know if
it is the best approach, but it solved the issue for us.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NMichael Trimarchi <trimarchimichael@yahoo.it>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f6121f4f
  43. 23 9月, 2008 1 次提交
  45. 22 9月, 2008 1 次提交