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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-07-12 02:24:45 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-07-18 00:59:06 +0300
commitcdacbe1f91264687af956e810278030f2ab5a3d0 (patch)
tree3a4e912e5c319329bc2a1e68b99ee041f0777150 /Documentation
parent32bb1c79996069ef9e4e53b428050749f9841c3f (diff)
downloadlinux-cdacbe1f91264687af956e810278030f2ab5a3d0.tar.xz
rcu: Add fastpath bypassing funnel locking
In the common case, there will be only one expedited grace period in the system at a given time, in which case it is not helpful to use funnel locking. This commit therefore adds a fastpath that bypasses funnel locking when the root ->exp_funnel_mutex is not held. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/RCU/trace.txt36
1 files changed, 10 insertions, 26 deletions
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 08651da15448..97f17e9decda 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -237,42 +237,26 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of
The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
-s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
+s=21872 wd0=0 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872
These fields are as follows:
-o "s" is the starting sequence number.
+o "s" is the sequence number, with an odd number indicating that
+ an expedited grace period is in progress.
-o "d" is the ending sequence number. When the starting and ending
- numbers differ, there is an expedited grace period in progress.
-
-o "w" is the number of times that the sequence numbers have been
- in danger of wrapping.
-
-o "tf" is the number of times that contention has resulted in a
- failure to begin an expedited grace period.
-
-o "wd1" and "wd2" are the number of times that an attempt to
- start an expedited grace period found that someone else had
- completed an expedited grace period that satisfies the
+o "wd0", "wd1", "wd2", and "wd3" are the number of times that an
+ attempt to start an expedited grace period found that someone
+ else had completed an expedited grace period that satisfies the
attempted request. "Our work is done."
-o "n" is number of times that contention was so great that
- the request was demoted from an expedited grace period to
- a normal grace period.
+o "n" is number of times that a concurrent CPU-hotplug operation
+ forced a fallback to a normal grace period.
+
+o "enq" is the number of quiescent states still outstanding.
o "sc" is the number of times that the attempt to start a
new expedited grace period succeeded.
-o "dt" is the number of times that we attempted to update
- the "d" counter.
-
-o "dl" is the number of times that we failed to update the "d"
- counter.
-
-o "dx" is the number of times that we succeeded in updating
- the "d" counter.
-
The output of "cat rcu/rcu_preempt/rcugp" looks as follows: