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    Subject[tip:sched/core] sched: Reset loop counters if all tasks are pinned and we need to redo load balance
    Commit-ID:  4d44f7090f8233f6994e7397679a32c81187506d
    Gitweb: http://git.kernel.org/tip/4d44f7090f8233f6994e7397679a32c81187506d
    Author: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
    AuthorDate: Tue, 19 Jun 2012 17:52:07 +0530
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 5 Jul 2012 21:09:10 +0200

    sched: Reset loop counters if all tasks are pinned and we need to redo load balance

    While load balancing, if all tasks on the source runqueue are pinned,
    we retry after excluding the corresponding source cpu. However, loop counters
    env.loop and env.loop_break are not reset before retrying, which can lead
    to failure in moving the tasks. In this patch we reset env.loop and
    env.loop_break to their inital values before we retry.

    Signed-off-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/4FE06EEF.2090709@linux.vnet.ibm.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/sched/fair.c | 5 ++++-
    1 files changed, 4 insertions(+), 1 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 39b5771..3f94840 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -4497,8 +4497,11 @@ more_balance:
    /* All tasks on this runqueue were pinned by CPU affinity */
    if (unlikely(env.flags & LBF_ALL_PINNED)) {
    cpumask_clear_cpu(cpu_of(busiest), cpus);
    - if (!cpumask_empty(cpus))
    + if (!cpumask_empty(cpus)) {
    + env.loop = 0;
    + env.loop_break = sched_nr_migrate_break;
    goto redo;
    + }
    goto out_balanced;
    }
    }

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