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  1. 06 Oct, 2011 4 commits
    • Peter Zijlstra's avatar
      sched: Wrap scheduler p->cpus_allowed access · fa17b507
      Peter Zijlstra authored 
      This task is preparatory for the migrate_disable() implementation, but
stands on its own and provides a cleanup.

It currently only converts those sites required for task-placement.
Kosaki-san once mentioned replacing cpus_allowed with a proper
cpumask_t instead of the NR_CPUS sized array it currently is, that
would also require something like this.
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Link: http://lkml.kernel.org/n/tip-e42skvaddos99psip0vce41o@git.kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
      fa17b507
    • Suresh Siddha's avatar
      sched: Request for idle balance during nohz idle load balance · 6eb57e0d
      Suresh Siddha authored 
      rq's idle_at_tick is set to idle/busy during the timer tick
depending on the cpu was idle or not. This will be used later in the load
balance that will be done in the softirq context (which is a process
context in -RT kernels).

For nohz kernels, for the cpu doing nohz idle load balance on behalf of
all the idle cpu's, its rq->idle_at_tick might have a stale value (which is
recorded when it got the timer tick presumably when it is busy).

As the nohz idle load balancing is also being done at the same place
as the regular load balancing, nohz idle load balancing was bailing out
when it sees rq's idle_at_tick not set.

Thus leading to poor system utilization.

Rename rq's idle_at_tick to idle_balance and set it when someone requests
for nohz idle balance on an idle cpu.
Reported-by: default avatarSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111003220934.892350549@sbsiddha-desk.sc.intel.comSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
      6eb57e0d
    • Suresh Siddha's avatar
      sched: Use resched IPI to kick off the nohz idle balance · ca38062e
      Suresh Siddha authored 
      Current use of smp call function to kick the nohz idle balance can deadlock
in this scenario.

1. cpu-A did a generic_exec_single() to cpu-B and after queuing its call single
data (csd) to the call single queue, cpu-A took a timer interrupt.  Actual IPI
to cpu-B to process the call single queue is not yet sent.

2. As part of the timer interrupt handler, cpu-A decided to kick cpu-B
for the idle load balancing (sets cpu-B's rq->nohz_balance_kick to 1)
and __smp_call_function_single() with nowait will queue the csd to the
cpu-B's queue. But the generic_exec_single() won't send an IPI to cpu-B
as the call single queue was not empty.

3. cpu-A is busy with lot of interrupts

4. Meanwhile cpu-B is entering and exiting idle and noticed that it has
it's rq->nohz_balance_kick set to '1'. So it will go ahead and do the
idle load balancer and clear its rq->nohz_balance_kick.

5. At this point, csd queued as part of the step-2 above is still locked
and waiting to be serviced on cpu-B.

6. cpu-A is still busy with interrupt load and now it got another timer
interrupt and as part of it decided to kick cpu-B for another idle load
balancing (as it finds cpu-B's rq->nohz_balance_kick cleared in step-4
above) and does __smp_call_function_single() with the same csd that is
still locked.

7. And we get a deadlock waiting for the csd_lock() in the
__smp_call_function_single().

Main issue here is that cpu-B can service the idle load balancer kick
request from cpu-A even with out receiving the IPI and this lead to
doing multiple __smp_call_function_single() on the same csd leading to
deadlock.

To kick a cpu, scheduler already has the reschedule vector reserved. Use
that mechanism (kick_process()) instead of using the generic smp call function
mechanism to kick off the nohz idle load balancing and avoid the deadlock.

   [ This issue is present from 2.6.35+ kernels, but marking it -stable
     only from v3.0+ as the proposed fix depends on the scheduler_ipi()
     that is introduced recently. ]
Reported-by: default avatarPrarit Bhargava <prarit@redhat.com>
Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Cc: stable@kernel.org # v3.0+
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111003220934.834943260@sbsiddha-desk.sc.intel.comSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
      ca38062e
    • Ingo Molnar's avatar
      Merge commit 'v3.1-rc9' into sched/core · 9243a169
      Ingo Molnar authored 
      Merge reason: pick up latest fixes.
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      9243a169
  3. 05 Oct, 2011 1 commit
  5. 04 Oct, 2011 22 commits
  7. 03 Oct, 2011 13 commits
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