Once we have the per cpu patchset merged we could do the following [it
even works without that patchset but the __this_cpu ops will not do
preemption checks]. Would this work?
Subject: rcu: Avoid irq disable in rcu_cpu_kthread
The use of this_cpu ops avoids numerous address calculations
and allows to avoid the irq enable/disable sequence through a
low latency non locking this_cpu_xchg.
Signed-off-by: Christoph Lameter <c...@linux.com>
Index: linux/kernel/rcu/tree_plugin.h
===================================================================
--- linux.orig/kernel/rcu/tree_plugin.h 2013-12-03 11:32:23.322999660 -0600
+++ linux/kernel/rcu/tree_plugin.h 2013-12-03 11:32:23.312999941 -0600
@@ -1417,33 +1417,29 @@ static int rcu_cpu_kthread_should_run(un
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
- unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
- char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
+ char work;
int spincnt;
for (spincnt = 0; spincnt < 10; spincnt++) {
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
local_bh_disable();
- *statusp = RCU_KTHREAD_RUNNING;
- this_cpu_inc(rcu_cpu_kthread_loops);
- local_irq_disable();
- work = *workp;
- *workp = 0;
- local_irq_enable();
+ __this_cpu_write(rcu_cpu_kthread_status, RCU_KTHREAD_RUNNING);
+ __this_cpu_inc(rcu_cpu_kthread_loops);
+ work = this_cpu_xchg(rcu_cpu_has_work, 0);
if (work)
rcu_kthread_do_work();
local_bh_enable();
- if (*workp == 0) {
+ if (__this_cpu_read(rcu_cpu_has_work) == 0) {
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
- *statusp = RCU_KTHREAD_WAITING;
+ __this_cpu_write(rcu_cpu_kthread_status,
RCU_KTHREAD_WAITING);
return;
}
}
- *statusp = RCU_KTHREAD_YIELDING;
+ __this_cpu_write(rcu_cpu_kthread_status, RCU_KTHREAD_YIELDING);
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
schedule_timeout_interruptible(2);
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
- *statusp = RCU_KTHREAD_WAITING;
+ __this_cpu_write(rcu_cpu_kthread_status, RCU_KTHREAD_WAITING);
}
/*
--
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