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rcu: Make force_quiescent_state() start grace period if needed

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Grace periods cannot be started while force_quiescent_state() is
active.  This is OK in that the affected CPUs will try again
later, but it does induce needless grace-period delays.  This
patch causes rcu_start_gp() to record a failed attempt to start
a grace period. When force_quiescent_state() prepares to return,
it then starts the grace period if there was such a failed
attempt.

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: <12626465501854-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-01-04 15:09:09 -08:00 committed by Ingo Molnar
parent 45f014c52e
commit 46a1e34eda
2 changed files with 13 additions and 0 deletions
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8
kernel/rcutree.c
View File

@ -660,6 +660,8 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
struct rcu_node *rnp = rcu_get_root(rsp);
if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
if (cpu_needs_another_gp(rsp, rdp))
rsp->fqs_need_gp = 1;
if (rnp->completed == rsp->completed) {
spin_unlock_irqrestore(&rnp->lock, flags);
return;
@ -1239,6 +1241,12 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
break;
}
rsp->fqs_active = 0;
if (rsp->fqs_need_gp) {
spin_unlock(&rsp->fqslock); /* irqs remain disabled */
rsp->fqs_need_gp = 0;
rcu_start_gp(rsp, flags); /* releases rnp->lock */
return;
}
spin_unlock(&rnp->lock); /* irqs remain disabled */
unlock_fqs_ret:
spin_unlock_irqrestore(&rsp->fqslock, flags);

5
kernel/rcutree.h
View File

@ -278,6 +278,11 @@ struct rcu_state {
/* Force QS state. */
u8 fqs_active; /* force_quiescent_state() */
/* is running. */
u8 fqs_need_gp; /* A CPU was prevented from */
/* starting a new grace */
/* period because */
/* force_quiescent_state() */
/* was running. */
long gpnum; /* Current gp number. */
long completed; /* # of last completed gp. */