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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2009-11-10 22:37:22 +0100 |
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committer | Ingo Molnar <mingo@elte.hu> | 2009-11-10 22:48:50 +0100 |
commit | c64ac3ce06558e534aec62b1fadeb0a3f111dac1 (patch) | |
tree | faee8cf2d5cb47aeac4999a1e2163491a8e03734 | |
parent | rcu: Rename dynticks_completed to completed_fqs (diff) | |
download | linux-c64ac3ce06558e534aec62b1fadeb0a3f111dac1.tar.xz linux-c64ac3ce06558e534aec62b1fadeb0a3f111dac1.zip |
rcu: Simplify association of quiescent states with grace periods
The rdp->passed_quiesc_completed fields are used to properly
associate the recorded quiescent state with a grace period. It
is OK to wrongly associate a given quiescent state with a
preceding grace period, but it is fatal to associate a given
quiescent state with a grace period that begins after the
quiescent state occurred. Grace periods are numbered, and the
following fields track them:
o ->gpnum is the number of the grace period currently in
progress, or the number of the last grace period to
complete if no grace period is currently in progress.
o ->completed is the number of the last grace period to
have completed.
These two fields are equal if there is no grace period in
progress, otherwise ->gpnum is one greater than ->completed.
But the rdp->passed_quiesc_completed field compared against
->completed, and if equal, the quiescent state is presumed to
count against the current grace period.
The earlier code copied rdp->completed to
rdp->passed_quiesc_completed, which has been made to work, but
is error-prone. In contrast, copying one less than rdp->gpnum
is guaranteed safe, because rdp->gpnum is not incremented until
after the start of the corresponding grace period. At the end of
the grace period, when ->completed has incremented, then any
quiescent periods recorded previously will be discarded.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12578890421011-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r-- | kernel/rcutree.c | 4 | ||||
-rw-r--r-- | kernel/rcutree_plugin.h | 2 |
2 files changed, 3 insertions, 3 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 26fc7807761d..d8024192c73b 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -100,7 +100,7 @@ void rcu_sched_qs(int cpu) struct rcu_data *rdp; rdp = &per_cpu(rcu_sched_data, cpu); - rdp->passed_quiesc_completed = rdp->completed; + rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; rcu_preempt_note_context_switch(cpu); @@ -111,7 +111,7 @@ void rcu_bh_qs(int cpu) struct rcu_data *rdp; rdp = &per_cpu(rcu_bh_data, cpu); - rdp->passed_quiesc_completed = rdp->completed; + rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; } diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index c03edf766357..52075da70549 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -67,7 +67,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed); static void rcu_preempt_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); - rdp->passed_quiesc_completed = rdp->completed; + rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; } |