| From | "Paul E. McKenney" <> | Subject | [PATCH v3 tip/core/rcu 11/18] rcu: Don't wake rcuc/X kthreads on NOCB CPUs | Date | Tue, 24 Jan 2017 13:51:22 -0800 |
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Chris Friesen notice that rcuc/X kthreads were consuming CPU even on NOCB CPUs. This makes no sense because the only purpose or these kthreads is to invoke normal (non-offloaded) callbacks, of which there will never be any on NOCB CPUs. This problem was due to a bug in cpu_has_callbacks_ready_to_invoke(), which should have been checking ->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly) checking ->nxttail[RCU_DONE_TAIL]. Because ->nxttail[RCU_DONE_TAIL] is never NULL, the only effect is to cause the rcuc/X kthread to execute when it should not do so.
This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL for NOCB CPUs.
Reported-by: Chris Friesen <chris.friesen@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d7b63b88434b..be2301238a23 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -611,7 +611,7 @@ static int cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) { return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] && - rdp->nxttail[RCU_DONE_TAIL] != NULL; + rdp->nxttail[RCU_NEXT_TAIL] != NULL; } /* -- 2.5.2
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