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    Subject[patch] RCU: introduce rcu_soon_pending() interface
    From: Heiko Carstens <heiko.carstens@de.ibm.com>

    Introduce rcu_soon_pending() interface. This can be used to tell if there
    will be a new rcu batch on a cpu soon by looking at the curlist pointer.
    This can be used to avoid to enter a tickless idle state where the cpu
    would miss that a new batch is ready when rcu_start_batch would be called
    on a different cpu.

    Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
    ---

    See also here: http://www.ussg.iu.edu/hypermail/linux/kernel/0604.3/0057.html
    Better solutions welcome :)

    include/linux/rcupdate.h | 1 +
    kernel/rcupdate.c | 8 ++++++++
    2 files changed, 9 insertions(+)

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 5673008..80bcbce 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -132,6 +132,7 @@ static inline void rcu_bh_qsctr_inc(int
    }

    extern int rcu_pending(int cpu);
    +extern int rcu_soon_pending(int cpu);

    /**
    * rcu_read_lock - mark the beginning of an RCU read-side critical section.
    diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
    index 13458bb..e8cf09f 100644
    --- a/kernel/rcupdate.c
    +++ b/kernel/rcupdate.c
    @@ -485,6 +485,14 @@ int rcu_pending(int cpu)
    __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
    }

    +int rcu_soon_pending(int cpu)
    +{
    + struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
    + struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
    +
    + return (!!rdp->curlist || !!rdp_bh->curlist);
    +}
    +
    void rcu_check_callbacks(int cpu, int user)
    {
    if (user ||
    -
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