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Commit 2d999e03 authored by Paul E. McKenney's avatar Paul E. McKenney
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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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 29494be7

Documentation/RCU/trace.txt

+4 −8
Original line number Diff line number Diff line
@@ -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

kernel/rcutree.c

+6 −4
Original line number Diff line number Diff line
@@ -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);

kernel/rcutree_plugin.h

+1 −1
Original line number Diff line number Diff line
@@ -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)

{