From cdacbe1f91264687af956e810278030f2ab5a3d0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 11 Jul 2015 16:24:45 -0700 Subject: 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 --- Documentation/RCU/trace.txt | 36 ++++++++++-------------------------- 1 file changed, 10 insertions(+), 26 deletions(-) (limited to 'Documentation/RCU') 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: -- cgit v1.2.3