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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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