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Date: Sat, 6 Nov 2010 19:05:30 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 10/12] rcu: update documentation/comments for Lai's adoption patch
Lai's RCU-callback immediate-adoption patch changes the RCU tracing
output, so update tracing.txt. Also update a few comments to clarify
the synchronization design.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
Documentation/RCU/trace.txt | 12 ++++--------
kernel/rcutree.c | 10 ++++++----
kernel/rcutree_plugin.h | 2 +-
3 files changed, 11 insertions(+), 13 deletions(-)
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index ff6d3f1..6a8c73f 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -134,7 +134,8 @@ o "ci" is the number of RCU callbacks that have been invoked for
been registered in absence of CPU-hotplug activity.
o "co" is the number of RCU callbacks that have been orphaned due to
- this CPU going offline.
+ this CPU going offline. These orphaned callbacks have been moved
+ to an arbitrarily chosen online CPU.
o "ca" is the number of RCU callbacks that have been adopted due to
other CPUs going offline. Note that ci+co-ca+ql is the number of
@@ -172,12 +173,12 @@ o "gpnum" is the number of grace periods that have started. It is
The output of "cat rcu/rcuhier" looks as follows, with very long lines:
-c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 oqlen=0
+c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
1/1 .>. 0:127 ^0
3/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
3/3f .>. 0:5 ^0 2/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3
rcu_bh:
-c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0 oqlen=0
+c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
0/1 .>. 0:127 ^0
0/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
0/3f .>. 0:5 ^0 0/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3
@@ -216,11 +217,6 @@ o "fqlh" is the number of calls to force_quiescent_state() that
exited immediately (without even being counted in nfqs above)
due to contention on ->fqslock.
-o "oqlen" is the number of callbacks on the "orphan" callback
- list. RCU callbacks are placed on this list by CPUs going
- offline, and are "adopted" either by the CPU helping the outgoing
- CPU or by the next rcu_barrier*() call, whichever comes first.
-
o Each element of the form "1/1 0:127 ^0" represents one struct
rcu_node. Each line represents one level of the hierarchy, from
root to leaves. It is best to think of the rcu_data structures
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 669d7fe..120820f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1668,7 +1668,9 @@ static void _rcu_barrier(struct rcu_state *rsp,
* decrement rcu_barrier_cpu_count -- otherwise the first CPU
* might complete its grace period before all of the other CPUs
* did their increment, causing this function to return too
- * early.
+ * early. Note that on_each_cpu() disables irqs, which prevents
+ * any CPUs from coming online or going offline until each online
+ * CPU has queued its RCU-barrier callback.
*/
atomic_set(&rcu_barrier_cpu_count, 1);
on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
@@ -1797,9 +1799,9 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
case CPU_DYING:
case CPU_DYING_FROZEN:
/*
- * The whole machine is "stopped" except this cpu, so we can
- * touch any data without introducing corruption. And we send
- * the callbacks to an attribute chosen online cpu.
+ * The whole machine is "stopped" except this CPU, so we can
+ * touch any data without introducing corruption. We send the
+ * dying CPU's callbacks to an arbitrarily chosen online CPU.
*/
rcu_send_cbs_to_online(&rcu_bh_state);
rcu_send_cbs_to_online(&rcu_sched_state);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 0de359b..643c8f6 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -774,7 +774,7 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
- * Move preemptable DYING RCU's callbacks to other online CPU.
+ * Move preemptable RCU's callbacks from dying CPU to other online CPU.
*/
static void rcu_preempt_send_cbs_to_online(void)
{
--
1.7.0.6
--
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