Messages in this thread Patch in this message | | | From | Joel Fernandes <> | Subject | [PATCH v3 3/4] rcu: Use better variable names in funnel locking loop | Date | Sun, 20 May 2018 21:42:19 -0700 |
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The funnel locking loop in rcu_start_this_gp uses rcu_root as a temporary variable while walking the combining tree. This causes a tiresome exercise of a code reader reminding themselves that rcu_root may not be root. Lets just call it rnp, and rename other variables as well to be more appropriate.
Original patch: https://patchwork.kernel.org/patch/10396577/
Signed-off-by: Joel Fernandes <joel@joelfernandes.org> --- kernel/rcu/tree.c | 48 ++++++++++++++++++++++++----------------------- 1 file changed, 25 insertions(+), 23 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0ffd41ba304f..879c67a31116 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1526,7 +1526,7 @@ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, /* * rcu_start_this_gp - Request the start of a particular grace period - * @rnp: The leaf node of the CPU from which to start. + * @rnp_start: The leaf node of the CPU from which to start. * @rdp: The rcu_data corresponding to the CPU from which to start. * @gp_seq_req: The gp_seq of the grace period to start. * @@ -1540,12 +1540,12 @@ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, * * Returns true if the GP thread needs to be awakened else false. */ -static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, +static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, unsigned long gp_seq_req) { bool ret = false; struct rcu_state *rsp = rdp->rsp; - struct rcu_node *rnp_root; + struct rcu_node *rnp, *rnp_root = NULL; /* * Use funnel locking to either acquire the root rcu_node @@ -1556,34 +1556,36 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, * scan the leaf rcu_node structures. Note that rnp->lock must * not be released. */ - raw_lockdep_assert_held_rcu_node(rnp); - trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startleaf")); - for (rnp_root = rnp; 1; rnp_root = rnp_root->parent) { - if (rnp_root != rnp) - raw_spin_lock_rcu_node(rnp_root); - if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_req) || - rcu_seq_started(&rnp_root->gp_seq, gp_seq_req) || - (rnp != rnp_root && - rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) { - trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, + raw_lockdep_assert_held_rcu_node(rnp_start); + trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf")); + for (rnp = rnp_start; 1; rnp = rnp->parent) { + if (rnp != rnp_start) + raw_spin_lock_rcu_node(rnp); + if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) || + rcu_seq_started(&rnp->gp_seq, gp_seq_req) || + (rnp != rnp_start && + rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) { + trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Prestarted")); goto unlock_out; } - rnp_root->gp_seq_needed = gp_seq_req; - if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { + rnp->gp_seq_needed = gp_seq_req; + if (rcu_seq_state(rcu_seq_current(&rnp_start->gp_seq))) { /* * We just marked the leaf, and a grace period * is in progress, which means that rcu_gp_cleanup() * will see the marking. Bail to reduce contention. */ - trace_rcu_this_gp(rnp, rdp, gp_seq_req, + trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startedleaf")); goto unlock_out; } - if (rnp_root != rnp && rnp_root->parent != NULL) - raw_spin_unlock_rcu_node(rnp_root); - if (!rnp_root->parent) + if (rnp != rnp_start && rnp->parent != NULL) + raw_spin_unlock_rcu_node(rnp); + if (!rnp->parent) { + rnp_root = rnp; break; /* At root, and perhaps also leaf. */ + } } /* If GP already in progress, just leave, otherwise start one. */ @@ -1601,11 +1603,11 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq")); ret = true; /* Caller must wake GP kthread. */ unlock_out: - if (rnp != rnp_root) - raw_spin_unlock_rcu_node(rnp_root); + if (rnp != rnp_start) + raw_spin_unlock_rcu_node(rnp); /* Push furthest requested GP to leaf node and rcu_data structure. */ - if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_req)) { - rnp->gp_seq_needed = gp_seq_req; + if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req)) { + rnp_start->gp_seq_needed = gp_seq_req; rdp->gp_seq_needed = gp_seq_req; } return ret; -- 2.17.0.441.gb46fe60e1d-goog
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