On Wed, Jul 01, 2015 at 12:03:52PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 30, 2015 at 02:48:27PM -0700, Paul E. McKenney wrote:
> > @@ -2121,17 +2137,24 @@ static int __noreturn rcu_gp_kthread(void *arg)
> > TPS("fqswait"));
> > rsp->gp_state = RCU_GP_WAIT_FQS;
> > ret = wait_event_interruptible_timeout(rsp->gp_wq,
> > - ((gf = READ_ONCE(rsp->gp_flags)) &
> > - RCU_GP_FLAG_FQS) ||
> > - (!READ_ONCE(rnp->qsmask) &&
> > - !rcu_preempt_blocked_readers_cgp(rnp)),
> > - j);
> > + ((gf = READ_ONCE(rsp->gp_flags)) &
> > + RCU_GP_FLAG_FQS) ||
> > + (!READ_ONCE(rnp->qsmask) &&
> > + !rcu_preempt_blocked_readers_cgp(rnp)) ||
> > + rcu_exp_gp_seq_done(rsp->exp_rsp,
> > + rsp->gp_exp_snap),
> > + j);
>
> How about using a helper function there?
>
> static inline bool rcu_gp_done(rsp, rnp)
> {
> /* Forced Quiescent State complete */
> if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)
> return true;
>
> /* QS not masked and not blocked by preempted readers */
> if (!READ_ONCE(rnp->qsmask) &&
> !rcu_preempt_blocked_readers_cgp(rnp))
> return true;
>
> /* Expedited Grace Period completed */
> if (rcu_exp_gp_seq_done(rsp))
> return true;
>
> return false;
> }
>
> ret = wait_event_interruptible_timeout(rsp->gp_wq,
> rcu_gp_done(rsp, rnp), j);
Fair point, and applies to the original as well, give or take comments
and naming. Please see below for the corresponding patch. Thoughts?
Thanx, Paul
------------------------------------------------------------------------
commit a8bb9abbf3690e507d61efe8144cec091ce5fb02
Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Date: Wed Jul 1 13:50:28 2015 -0700
rcu: Pull out wait_event*() condition into helper function
The condition for the wait_event_interruptible_timeout() that waits
to do the next force-quiescent-state scan is a bit ornate:
((gf = READ_ONCE(rsp->gp_flags)) &
RCU_GP_FLAG_FQS) ||
(!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp))
This commit therefore pulls this condition out into a helper function
and comments its component conditions.
Reported-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4992bfd360b6..2afb8e8c5134 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1904,6 +1904,26 @@ static int rcu_gp_init(struct rcu_state *rsp)
}
/*
+ * Helper function for wait_event_interruptible_timeout() wakeup
+ * at force-quiescent-state time.
+ */
+static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
+{
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ /* Someone like call_rcu() requested a force-quiescent-state scan. */
+ *gfp = READ_ONCE(rsp->gp_flags);
+ if (*gfp & RCU_GP_FLAG_FQS)
+ return true;
+
+ /* The current grace period has completed. */
+ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
+ return true;
+
+ return false;
+}
+
+/*
* Do one round of quiescent-state forcing.
*/
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
@@ -2067,11 +2087,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
TPS("fqswait"));
rsp->gp_state = RCU_GP_WAIT_FQS;
ret = wait_event_interruptible_timeout(rsp->gp_wq,
- ((gf = READ_ONCE(rsp->gp_flags)) &
- RCU_GP_FLAG_FQS) ||
- (!READ_ONCE(rnp->qsmask) &&
- !rcu_preempt_blocked_readers_cgp(rnp)),
- j);
+ rcu_gp_fqs_check_wake(rsp, &gf), j);
rsp->gp_state = RCU_GP_DONE_FQS;
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */
--
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