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rcu: Optimize cond_resched_rcu_qs() 

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>
This commit is contained in:
Paul E. McKenney 2014-10-04 03:43:41 -07:00
parent 1a6c9b2675
commit b6331ae8af
1 changed files with 2 additions and 2 deletions
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4
include/linux/rcupdate.h
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@ -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)