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    Subject[RFC PATCH 1/8] Convert the RCU tasklet into a softirq
    I believe this was originally done by Dipankar Sarma. I pulled these
    changes from the -rt kernel.

    For better preformance, RCU should use a softirq instead of a
    tasklet.

    From: Dipankar Sarma <dipankar@in.ibm.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

    Index: linux-2.6-test/include/linux/interrupt.h
    ===================================================================
    --- linux-2.6-test.orig/include/linux/interrupt.h
    +++ linux-2.6-test/include/linux/interrupt.h
    @@ -245,6 +245,9 @@ enum
    #ifdef CONFIG_HIGH_RES_TIMERS
    HRTIMER_SOFTIRQ,
    #endif
    + RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */
    + /* Entries after this are ignored in split softirq mode */
    + MAX_SOFTIRQ,
    };

    /* softirq mask and active fields moved to irq_cpustat_t in
    Index: linux-2.6-test/kernel/rcupdate.c
    ===================================================================
    --- linux-2.6-test.orig/kernel/rcupdate.c
    +++ linux-2.6-test/kernel/rcupdate.c
    @@ -67,7 +67,6 @@ 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;
    @@ -253,7 +252,7 @@ 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);
    }

    /*
    @@ -405,7 +404,6 @@ 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
    @@ -417,7 +415,7 @@ 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)
    @@ -462,7 +460,7 @@ 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));
    @@ -526,7 +524,7 @@ 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,
    @@ -549,7 +547,7 @@ 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 __cpuinit rcu_cpu_notify(struct notifier_block *self,
    --
    -
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