rcu/trace: Use gp_seq_req in acceleration's rcu_grace_period tracepoint

During acceleration of CB, the rsp's gp_seq is rcu_seq_snap'd. This is
the value used for acceleration - it is the value of gp_seq at which it
is safe the execute all callbacks in the callback list.

The rdp's gp_seq is not very useful for this scenario. Make
rcu_grace_period report the gp_seq_req instead as it allows one to
reason about how the acceleration works.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index eb36779697ca974950c0197e4ddc7b62865d04bc..896912034982197341a6d79dae217f69a0221efe 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1483,9 +1483,10 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 
        /* Trace depending on how much we were able to accelerate. */
        if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
-               trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccWaitCB"));
+               trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
        else
-               trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccReadyCB"));
+               trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
+
        return ret;
 }