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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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