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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-11-30 22:21:21 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-01-23 22:44:18 +0300
commit3a19b46a5c17b12ef0691df19c676ba3da330a57 (patch)
treeb9effecf9064beba8b6d55fa5a7c1fd1b56a72c4 /include/trace/events/rcu.h
parent02a5c550b2738f2bfea8e1e00aa75944d71c9e18 (diff)
downloadlinux-3a19b46a5c17b12ef0691df19c676ba3da330a57.tar.xz
rcu: Check cond_resched_rcu_qs() state less often to reduce GP overhead
Commit 4a81e8328d37 ("rcu: Reduce overhead of cond_resched() checks for RCU") moved quiescent-state generation out of cond_resched() and commit bde6c3aa9930 ("rcu: Provide cond_resched_rcu_qs() to force quiescent states in long loops") introduced cond_resched_rcu_qs(), and commit 5cd37193ce85 ("rcu: Make cond_resched_rcu_qs() apply to normal RCU flavors") introduced the per-CPU rcu_qs_ctr variable, which is frequently polled by the RCU core state machine. This frequent polling can increase grace-period rate, which in turn increases grace-period overhead, which is visible in some benchmarks (for example, the "open1" benchmark in Anton Blanchard's "will it scale" suite). This commit therefore reduces the rate at which rcu_qs_ctr is polled by moving that polling into the force-quiescent-state (FQS) machinery, and by further polling it only after the grace period has been in effect for at least jiffies_till_sched_qs jiffies. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'include/trace/events/rcu.h')
-rw-r--r--include/trace/events/rcu.h10
1 files changed, 5 insertions, 5 deletions
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 9d4f9b3a2b7b..e3facb356838 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -385,11 +385,11 @@ TRACE_EVENT(rcu_quiescent_state_report,
/*
* Tracepoint for quiescent states detected by force_quiescent_state().
- * These trace events include the type of RCU, the grace-period number
- * that was blocked by the CPU, the CPU itself, and the type of quiescent
- * state, which can be "dti" for dyntick-idle mode, "ofl" for CPU offline,
- * or "kick" when kicking a CPU that has been in dyntick-idle mode for
- * too long.
+ * These trace events include the type of RCU, the grace-period number that
+ * was blocked by the CPU, the CPU itself, and the type of quiescent state,
+ * which can be "dti" for dyntick-idle mode, "ofl" for CPU offline, "kick"
+ * when kicking a CPU that has been in dyntick-idle mode for too long, or
+ * "rqc" if the CPU got a quiescent state via its rcu_qs_ctr.
*/
TRACE_EVENT(rcu_fqs,