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    Subject[PATCH -tip] v3 Simplify rcu_pending()/rcu_check_callbacks() API
    Date
    From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    All calls from outside RCU are of the form:

    if (rcu_pending(cpu))
    rcu_check_callbacks(cpu, user);

    This is silly, instead we put a call to rcu_pending() in
    rcu_check_callbacks(), and then make the outside calls be to
    rcu_check_callbacks(). This cuts down on the code a bit and
    also gives the compiler a better chance of optimizing.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    arch/ia64/xen/time.c | 3 +--
    include/linux/rcupreempt.h | 1 -
    include/linux/rcutree.h | 1 -
    kernel/rcupreempt.c | 10 ++++++++--
    kernel/rcutree.c | 5 ++++-
    kernel/timer.c | 3 +--
    6 files changed, 14 insertions(+), 9 deletions(-)

    diff --git a/arch/ia64/xen/time.c b/arch/ia64/xen/time.c
    index fb83326..dbeadb9 100644
    --- a/arch/ia64/xen/time.c
    +++ b/arch/ia64/xen/time.c
    @@ -133,8 +133,7 @@ consider_steal_time(unsigned long new_itm)
    account_idle_ticks(blocked);
    run_local_timers();

    - if (rcu_pending(cpu))
    - rcu_check_callbacks(cpu, user_mode(get_irq_regs()));
    + rcu_check_callbacks(cpu, user_mode(get_irq_regs()));

    scheduler_tick();
    run_posix_cpu_timers(p);
    diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
    index 6c9dd9c..aff4772 100644
    --- a/include/linux/rcupreempt.h
    +++ b/include/linux/rcupreempt.h
    @@ -66,7 +66,6 @@ extern void call_rcu_sched(struct rcu_head *head,

    extern void __rcu_read_lock(void);
    extern void __rcu_read_unlock(void);
    -extern int rcu_pending(int cpu);
    extern int rcu_needs_cpu(int cpu);

    #define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
    diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
    index 8a0222c..c739d90 100644
    --- a/include/linux/rcutree.h
    +++ b/include/linux/rcutree.h
    @@ -33,7 +33,6 @@
    extern void rcu_sched_qs(int cpu);
    extern void rcu_bh_qs(int cpu);

    -extern int rcu_pending(int cpu);
    extern int rcu_needs_cpu(int cpu);

    static inline void __rcu_read_lock(void)
    diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
    index 0eef9b7..2ab2146 100644
    --- a/kernel/rcupreempt.c
    +++ b/kernel/rcupreempt.c
    @@ -159,6 +159,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched
    .dynticks = 1,
    };

    +static int rcu_pending(int cpu);
    +
    void rcu_sched_qs(int cpu)
    {
    struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
    @@ -961,7 +963,10 @@ static void rcu_check_mb(int cpu)
    void rcu_check_callbacks(int cpu, int user)
    {
    unsigned long flags;
    - struct rcu_data *rdp = RCU_DATA_CPU(cpu);
    + struct rcu_data *rdp;
    +
    + if (!rcu_pending(cpu))
    + return; /* if nothing for RCU to do. */

    /*
    * If this CPU took its interrupt from user mode or from the
    @@ -976,6 +981,7 @@ void rcu_check_callbacks(int cpu, int user)
    * CPUs to happen after any such write.
    */

    + rdp = RCU_DATA_CPU(cpu);
    if (user ||
    (idle_cpu(cpu) && !in_softirq() &&
    hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
    @@ -1382,7 +1388,7 @@ int rcu_needs_cpu(int cpu)
    rdp->waitschedlist != NULL);
    }

    -int rcu_pending(int cpu)
    +static int rcu_pending(int cpu)
    {
    struct rcu_data *rdp = RCU_DATA_CPU(cpu);

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index 7c51508..4ce3adc 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -111,6 +111,7 @@ static int qhimark = 10000; /* If this many pending, ignore blimit. */
    static int qlowmark = 100; /* Once only this many pending, use blimit. */

    static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
    +static int rcu_pending(int cpu);

    /*
    * Return the number of RCU-sched batches processed thus far for debug & stats.
    @@ -974,6 +975,8 @@ static void rcu_do_batch(struct rcu_data *rdp)
    */
    void rcu_check_callbacks(int cpu, int user)
    {
    + if (!rcu_pending(cpu))
    + return; /* if nothing for RCU to do. */
    if (user ||
    (idle_cpu(cpu) && rcu_scheduler_active &&
    !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
    @@ -1329,7 +1332,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
    * by the current CPU, returning 1 if so. This function is part of the
    * RCU implementation; it is -not- an exported member of the RCU API.
    */
    -int rcu_pending(int cpu)
    +static int rcu_pending(int cpu)
    {
    return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
    __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu));
    diff --git a/kernel/timer.c b/kernel/timer.c
    index a7f07d5..a3d25f4 100644
    --- a/kernel/timer.c
    +++ b/kernel/timer.c
    @@ -1156,8 +1156,7 @@ void update_process_times(int user_tick)
    /* Note: this timer irq context must be accounted for as well. */
    account_process_tick(p, user_tick);
    run_local_timers();
    - if (rcu_pending(cpu))
    - rcu_check_callbacks(cpu, user_tick);
    + rcu_check_callbacks(cpu, user_tick);
    printk_tick();
    scheduler_tick();
    run_posix_cpu_timers(p);
    --
    1.5.2.5


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