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Subject[PATCH tip/core/rcu 6/9] rcu: Optimize cond_resched_rcu_qs()
Date
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The current implementation of cond_resched_rcu_qs() can invoke
rcu_note_voluntary_context_switch() twice in the should_resched()
case, once via the call to __schedule() and once directly. However, as
noted by Joe Lawrence in a patch to the team subsystem, cond_resched()
returns an indication as to whether or not the call to __schedule()
actually happened. This commit therefore changes cond_resched_rcu_qs()
so as to invoke rcu_note_voluntary_context_switch() only when __schedule()
was not called.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a033d8b55773..36ea3ba5c516 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -348,8 +348,8 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
*/
#define cond_resched_rcu_qs() \
do { \
- rcu_note_voluntary_context_switch(current); \
- cond_resched(); \
+ if (!cond_resched()) \
+ rcu_note_voluntary_context_switch(current); \
} while (0)

#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
--
1.8.1.5


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