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    SubjectRe: [PATCH 2/4] RCU: use a separate softirq

    Finally, RCU gets its own softirq. With it being used extensively,
    the per-cpu tasklet used earlier was just a softirq with overheads.
    This makes things more efficient.

    Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
    ---


    include/linux/interrupt.h | 3 ++-
    kernel/rcuclassic.c | 12 +++++-------
    2 files changed, 7 insertions(+), 8 deletions(-)

    diff -puN kernel/rcuclassic.c~rcu-softirq kernel/rcuclassic.c
    --- linux-2.6.18-rc3-rcu/kernel/rcuclassic.c~rcu-softirq 2006-08-27 01:01:15.000000000 +0530
    +++ linux-2.6.18-rc3-rcu-dipankar/kernel/rcuclassic.c 2006-08-27 01:01:15.000000000 +0530
    @@ -69,7 +69,6 @@ DEFINE_PER_CPU(struct rcu_data, rcu_data
    DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };

    /* Fake initialization required by compiler */
    -static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
    static int blimit = 10;
    static int qhimark = 10000;
    static int qlowmark = 100;
    @@ -212,7 +211,7 @@ static void rcu_do_batch(struct rcu_data
    if (!rdp->donelist)
    rdp->donetail = &rdp->donelist;
    else
    - tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
    + raise_softirq(RCU_SOFTIRQ);
    }

    /*
    @@ -363,7 +362,6 @@ static void rcu_offline_cpu(int cpu)
    &per_cpu(rcu_bh_data, cpu));
    put_cpu_var(rcu_data);
    put_cpu_var(rcu_bh_data);
    - tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
    }

    #else
    @@ -375,7 +373,7 @@ static void rcu_offline_cpu(int cpu)
    #endif

    /*
    - * This does the RCU processing work from tasklet context.
    + * This does the RCU processing work from softirq context.
    */
    static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
    struct rcu_data *rdp)
    @@ -420,7 +418,7 @@ static void __rcu_process_callbacks(stru
    rcu_do_batch(rdp);
    }

    -static void rcu_process_callbacks(unsigned long unused)
    +static void rcu_process_callbacks(struct softirq_action *unused)
    {
    __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
    __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
    @@ -484,7 +482,7 @@ void rcu_check_callbacks(int cpu, int us
    rcu_bh_qsctr_inc(cpu);
    } else if (!in_softirq())
    rcu_bh_qsctr_inc(cpu);
    - tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
    + raise_softirq(RCU_SOFTIRQ);
    }

    static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
    @@ -507,7 +505,7 @@ static void __devinit rcu_online_cpu(int

    rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
    rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
    - tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
    + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
    }

    static int __devinit rcu_cpu_notify(struct notifier_block *self,
    diff -puN include/linux/interrupt.h~rcu-softirq include/linux/interrupt.h
    --- linux-2.6.18-rc3-rcu/include/linux/interrupt.h~rcu-softirq 2006-08-27 01:01:15.000000000 +0530
    +++ linux-2.6.18-rc3-rcu-dipankar/include/linux/interrupt.h 2006-08-27 01:01:15.000000000 +0530
    @@ -219,7 +219,8 @@ enum
    NET_TX_SOFTIRQ,
    NET_RX_SOFTIRQ,
    BLOCK_SOFTIRQ,
    - TASKLET_SOFTIRQ
    + TASKLET_SOFTIRQ,
    + RCU_SOFTIRQ /* Preferable RCU should always be the last softirq */
    };

    /* softirq mask and active fields moved to irq_cpustat_t in
    _
    -
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