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rcu: merge TREE_PREEPT_RCU blocked_tasks[] lists
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Combine the current TREE_PREEMPT_RCU ->blocked_tasks[] lists in the
rcu_node structure into a single ->blkd_tasks list with ->gp_tasks
and ->exp_tasks tail pointers.  This is in preparation for RCU priority
boosting, which will add a third dimension to the combinatorial explosion
in the ->blocked_tasks[] case, but simply a third pointer in the new
->blkd_tasks case.

Also update documentation to reflect blocked_tasks[] merge

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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Paul E. McKenney authored and Paul E. McKenney committed May 6, 2011
1 parent e59fb31 commit 12f5f52
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29 changes: 18 additions & 11 deletions Documentation/RCU/trace.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -166,14 +166,14 @@ 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
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
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
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
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

This is once again split into "rcu_sched" and "rcu_bh" portions,
and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
Expand Down Expand Up @@ -232,13 +232,20 @@ o Each element of the form "1/1 0:127 ^0" represents one struct
current grace period.

o The characters separated by the ">" indicate the state
of the blocked-tasks lists. A "T" preceding the ">"
of the blocked-tasks lists. A "G" preceding the ">"
indicates that at least one task blocked in an RCU
read-side critical section blocks the current grace
period, while a "." preceding the ">" indicates otherwise.
The character following the ">" indicates similarly for
the next grace period. A "T" should appear in this
field only for rcu-preempt.
period, while a "E" preceding the ">" indicates that
at least one task blocked in an RCU read-side critical
section blocks the current expedited grace period.
A "T" character following the ">" indicates that at
least one task is blocked within an RCU read-side
critical section, regardless of whether any current
grace period (expedited or normal) is inconvenienced.
A "." character appears if the corresponding condition
does not hold, so that "..>." indicates that no tasks
are blocked. In contrast, "GE>T" indicates maximal
inconvenience from blocked tasks.

o The numbers separated by the ":" are the range of CPUs
served by this struct rcu_node. This can be helpful
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5 changes: 1 addition & 4 deletions kernel/rcutree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1901,10 +1901,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
j / rsp->levelspread[i - 1];
}
rnp->level = i;
INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
INIT_LIST_HEAD(&rnp->blkd_tasks);
}
}

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21 changes: 15 additions & 6 deletions kernel/rcutree.h
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ struct rcu_node {
/* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */
/* structure. */
unsigned long expmask; /* Groups that have ->blocked_tasks[] */
unsigned long expmask; /* Groups that have ->blkd_tasks */
/* elements that need to drain to allow the */
/* current expedited grace period to */
/* complete (only for TREE_PREEMPT_RCU). */
Expand All @@ -120,11 +120,20 @@ struct rcu_node {
u8 grpnum; /* CPU/group number for next level up. */
u8 level; /* root is at level 0. */
struct rcu_node *parent;
struct list_head blocked_tasks[4];
/* Tasks blocked in RCU read-side critsect. */
/* Grace period number (->gpnum) x blocked */
/* by tasks on the (x & 0x1) element of the */
/* blocked_tasks[] array. */
struct list_head blkd_tasks;
/* Tasks blocked in RCU read-side critical */
/* section. Tasks are placed at the head */
/* of this list and age towards the tail. */
struct list_head *gp_tasks;
/* Pointer to the first task blocking the */
/* current grace period, or NULL if there */
/* is no such task. */
struct list_head *exp_tasks;
/* Pointer to the first task blocking the */
/* current expedited grace period, or NULL */
/* if there is no such task. If there */
/* is no current expedited grace period, */
/* then there can cannot be any such task. */
} ____cacheline_internodealigned_in_smp;

/*
Expand Down
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