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    SubjectRe: [PATCH 2/4] RCU: use a separate softirq
    On Mon, Aug 28, 2006 at 09:41:12PM +0530, Dipankar Sarma wrote:
    >
    > 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.

    Acked-by: Paul E. McKenney <paulmck@us.ibm.com>

    > 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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