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Preempt-RCU: Use softirq instead of tasklets for

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This patch makes RCU use softirq instead of tasklets.

It also adds a memory barrier after raising the softirq
inorder to ensure that the cpu sees the most recently updated
value of rcu->cur while processing callbacks.
The discussion of the related theoretical race pointed out
by James Huang can be found here --> http://lkml.org/lkml/2007/11/20/603

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dipankar Sarma 2008-01-25 21:08:23 +01:00 committed by Ingo Molnar
parent c49443c538
commit c2d727aa2f
2 changed files with 18 additions and 8 deletions
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1
include/linux/interrupt.h
View file

@ -256,6 +256,7 @@ enum
#ifdef CONFIG_HIGH_RES_TIMERS #ifdef CONFIG_HIGH_RES_TIMERS
HRTIMER_SOFTIRQ, HRTIMER_SOFTIRQ,
#endif #endif
RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */
}; };
/* softirq mask and active fields moved to irq_cpustat_t in /* softirq mask and active fields moved to irq_cpustat_t in

25
kernel/rcupdate.c
View file

@ -73,8 +73,6 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; 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 blimit = 10;
static int qhimark = 10000; static int qhimark = 10000;
static int qlowmark = 100; static int qlowmark = 100;
@ -231,6 +229,18 @@ void rcu_barrier(void)
} }
EXPORT_SYMBOL_GPL(rcu_barrier); EXPORT_SYMBOL_GPL(rcu_barrier);
/* Raises the softirq for processing rcu_callbacks. */
static inline void raise_rcu_softirq(void)
{
raise_softirq(RCU_SOFTIRQ);
/*
* The smp_mb() here is required to ensure that this cpu's
* __rcu_process_callbacks() reads the most recently updated
* value of rcu->cur.
*/
smp_mb();
}
/* /*
* Invoke the completed RCU callbacks. They are expected to be in * Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list. * a per-cpu list.
@ -260,7 +270,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (!rdp->donelist) if (!rdp->donelist)
rdp->donetail = &rdp->donelist; rdp->donetail = &rdp->donelist;
else else
tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); raise_rcu_softirq();
} }
/* /*
@ -412,7 +422,6 @@ static void rcu_offline_cpu(int cpu)
&per_cpu(rcu_bh_data, cpu)); &per_cpu(rcu_bh_data, cpu));
put_cpu_var(rcu_data); put_cpu_var(rcu_data);
put_cpu_var(rcu_bh_data); put_cpu_var(rcu_bh_data);
tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
} }
#else #else
@ -424,7 +433,7 @@ static void rcu_offline_cpu(int cpu)
#endif #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, static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp) struct rcu_data *rdp)
@ -469,7 +478,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
rcu_do_batch(rdp); 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_ctrlblk, &__get_cpu_var(rcu_data));
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
@ -533,7 +542,7 @@ void rcu_check_callbacks(int cpu, int user)
rcu_bh_qsctr_inc(cpu); rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq()) } else if (!in_softirq())
rcu_bh_qsctr_inc(cpu); rcu_bh_qsctr_inc(cpu);
tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); raise_rcu_softirq();
} }
static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
@ -556,7 +565,7 @@ static void __cpuinit rcu_online_cpu(int cpu)
rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_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, static int __cpuinit rcu_cpu_notify(struct notifier_block *self,