[PATCH 2/3] rcu/trace: Use gp_seq_req in acceleration's rcu_grace_period tracepoint

Joel Fernandes (Google)
2020-06-19T01:36:53Z

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>
---
kernel/rcu/tree.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9ef68dd249e1d..d0988a1c1079d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1464,9 +1464,10 @@ 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;
}

--
2.27.0.111.gc72c7da667-goog