aboutsummaryrefslogtreecommitdiffstats
path: root/kernel
diff options
context:
space:
mode:
authorDipankar Sarma <dipankar@in.ibm.com>2008-01-25 21:08:23 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-25 21:08:23 +0100
commitc2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82 (patch)
tree76b570288a72c1337920c5e60682316c554f00ee /kernel
parentsched: remove some old cpuset logic (diff)
downloadlinux-dev-c2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82.tar.xz
linux-dev-c2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82.zip
Preempt-RCU: Use softirq instead of tasklets for
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcupdate.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f2c1a04e9b18..4dfa0b792efa 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -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_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;
@@ -231,6 +229,18 @@ void rcu_barrier(void)
}
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
* a per-cpu list.
@@ -260,7 +270,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (!rdp->donelist)
rdp->donetail = &rdp->donelist;
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));
put_cpu_var(rcu_data);
put_cpu_var(rcu_bh_data);
- tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
}
#else
@@ -424,7 +433,7 @@ 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)
@@ -469,7 +478,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
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));
@@ -533,7 +542,7 @@ void rcu_check_callbacks(int cpu, int user)
rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq())
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,
@@ -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_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,