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    Subject[PATCH v2] sched/fair: fix update the nohz.next_balance even if we haven't done any load balance
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    As Srikar pointed out (https://lkml.org/lkml/2015/3/27/26):

    | With the current code when the ilb cpus are not free:
    | - We would be updating the nohz.next_balance even through we havent done
    | any load balance.
    | - We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.

    This patch fix it by adding need_resched check with the idle check, and
    keep the need_resched check in for loop to catch ilb get busy.

    Suggested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Reviewed-by: Jason Low <jason.low2@hp.com>
    Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
    ---
    kernel/sched/fair.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 0576ce0..788e42f 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -7638,7 +7638,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
    struct rq *rq;
    int balance_cpu;

    - if (idle != CPU_IDLE ||
    + if (idle != CPU_IDLE || need_resched() ||
    !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
    goto end;

    --
    1.9.1


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