Re: [RFC PATCH 1/5 v2] Convert the RCU tasklet into a softirq

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Jun 22, 2007 at 02:20:52PM -0400, Steven Rostedt wrote:
> 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>

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

> 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,
> 
> --