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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-10-07 09:10:48 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-12-04 12:27:31 -0800
commit46a5d164db53ba6066b11889abb7fa6bddbe5cf7 (patch)
tree37e726508f20e8dd951f04dd3266be912abc5b44 /kernel/rcu/tree.c
parentf0f2e7d307fff226e0c1df5a07101a1216a46d8a (diff)
downloadlinux-sh-46a5d164db53ba6066b11889abb7fa6bddbe5cf7.tar.gz
rcu: Stop disabling interrupts in scheduler fastpaths
We need the scheduler's fastpaths to be, well, fast, and unnecessarily disabling and re-enabling interrupts is not necessarily consistent with this goal. Especially given that there are regions of the scheduler that already have interrupts disabled. This commit therefore moves the call to rcu_note_context_switch() to one of the interrupts-disabled regions of the scheduler, and removes the now-redundant disabling and re-enabling of interrupts from rcu_note_context_switch() and the functions it calls. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Shift rcu_note_context_switch() to avoid deadlock, as suggested by Peter Zijlstra. ]
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r--kernel/rcu/tree.c27
1 files changed, 12 insertions, 15 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ed3bc0578cc5..93941d3434ad 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -242,8 +242,6 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
*/
void rcu_sched_qs(void)
{
- unsigned long flags;
-
if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
return;
trace_rcu_grace_period(TPS("rcu_sched"),
@@ -252,13 +250,9 @@ void rcu_sched_qs(void)
__this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
return;
- local_irq_save(flags);
- if (__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) {
- __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
- rcu_report_exp_rdp(&rcu_sched_state,
- this_cpu_ptr(&rcu_sched_data), true);
- }
- local_irq_restore(flags);
+ __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
+ rcu_report_exp_rdp(&rcu_sched_state,
+ this_cpu_ptr(&rcu_sched_data), true);
}
void rcu_bh_qs(void)
@@ -295,17 +289,16 @@ EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
* We inform the RCU core by emulating a zero-duration dyntick-idle
* period, which we in turn do by incrementing the ->dynticks counter
* by two.
+ *
+ * The caller must have disabled interrupts.
*/
static void rcu_momentary_dyntick_idle(void)
{
- unsigned long flags;
struct rcu_data *rdp;
struct rcu_dynticks *rdtp;
int resched_mask;
struct rcu_state *rsp;
- local_irq_save(flags);
-
/*
* Yes, we can lose flag-setting operations. This is OK, because
* the flag will be set again after some delay.
@@ -335,13 +328,12 @@ static void rcu_momentary_dyntick_idle(void)
smp_mb__after_atomic(); /* Later stuff after QS. */
break;
}
- local_irq_restore(flags);
}
/*
* Note a context switch. This is a quiescent state for RCU-sched,
* and requires special handling for preemptible RCU.
- * The caller must have disabled preemption.
+ * The caller must have disabled interrupts.
*/
void rcu_note_context_switch(void)
{
@@ -371,9 +363,14 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
*/
void rcu_all_qs(void)
{
+ unsigned long flags;
+
barrier(); /* Avoid RCU read-side critical sections leaking down. */
- if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
+ if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
+ local_irq_save(flags);
rcu_momentary_dyntick_idle();
+ local_irq_restore(flags);
+ }
this_cpu_inc(rcu_qs_ctr);
barrier(); /* Avoid RCU read-side critical sections leaking up. */
}