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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-03-02 16:35:27 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-05-15 10:27:29 -0700
commitcee4393989333795ae04dc9f3b83a578afe3fca6 (patch)
tree9b3afa8f132956c603f83a1fb098f8d30a81d7c1 /include/linux/rcupdate.h
parent6fba2b3767ea6e3e1204855031492415cc4dce4f (diff)
downloadlwn-cee4393989333795ae04dc9f3b83a578afe3fca6.tar.gz
lwn-cee4393989333795ae04dc9f3b83a578afe3fca6.zip
rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs()
Commit e31d28b6ab8f ("trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched()") substituted cond_resched() for the earlier call to cond_resched_rcu_qs(). However, the new-age cond_resched() does not do anything to help RCU-tasks grace periods because (1) RCU-tasks is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a complete no-op when preemption is enabled. This situation results in hangs when running the trace benchmarks. A number of potential fixes were discussed on LKML (https://lkml.kernel.org/r/20180224151240.0d63a059@vmware.local.home), including making cond_resched() not be a no-op; making cond_resched() not be a no-op, but only when running tracing benchmarks; reverting the aforementioned commit (which works because cond_resched_rcu_qs() does provide an RCU-tasks quiescent state; and adding a call to the scheduler/RCU rcu_note_voluntary_context_switch() function. All were deemed unsatisfactory, either due to added cond_resched() overhead or due to magic functions inviting cargo culting. This commit renames cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs(), which provides a clear hint as to what this function is doing and why and where it should be used, and then replaces the call to cond_resched() with cond_resched_tasks_rcu_qs() in the trace benchmark's benchmark_event_kthread() function. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Nicholas Piggin <npiggin@gmail.com>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r--include/linux/rcupdate.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 36360d07f25b..19d235fefdb9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -188,13 +188,13 @@ static inline void exit_tasks_rcu_finish(void) { }
#endif /* #else #ifdef CONFIG_TASKS_RCU */
/**
- * cond_resched_rcu_qs - Report potential quiescent states to RCU
+ * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
*
* This macro resembles cond_resched(), except that it is defined to
* report potential quiescent states to RCU-tasks even if the cond_resched()
* machinery were to be shut off, as some advocate for PREEMPT kernels.
*/
-#define cond_resched_rcu_qs() \
+#define cond_resched_tasks_rcu_qs() \
do { \
if (!cond_resched()) \
rcu_note_voluntary_context_switch_lite(current); \