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Subject[PATCH RFC 4/8] rcu: Get rid of old c variable from places in tree RCU
Date
The 'c' variable was used previously to store the grace period
that is being requested. However it is not very meaningful for
a code reader, this patch replaces it with gp_seq_start indicating that
this is the grace period that was requested. Also updating tracing with
the new name.

Just a clean up patch, no logical change.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
include/trace/events/rcu.h | 15 ++++++------
kernel/rcu/tree.c | 47 ++++++++++++++++++++++----------------
2 files changed, 35 insertions(+), 27 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index ce9d1a1cac78..539900a9f8c7 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -103,15 +103,16 @@ TRACE_EVENT(rcu_grace_period,
*/
TRACE_EVENT(rcu_future_grace_period,

- TP_PROTO(const char *rcuname, unsigned long gp_seq, unsigned long c,
- u8 level, int grplo, int grphi, const char *gpevent),
+ TP_PROTO(const char *rcuname, unsigned long gp_seq,
+ unsigned long gp_seq_start, u8 level, int grplo, int grphi,
+ const char *gpevent),

- TP_ARGS(rcuname, gp_seq, c, level, grplo, grphi, gpevent),
+ TP_ARGS(rcuname, gp_seq, gp_seq_start, level, grplo, grphi, gpevent),

TP_STRUCT__entry(
__field(const char *, rcuname)
__field(unsigned long, gp_seq)
- __field(unsigned long, c)
+ __field(unsigned long, gp_seq_start)
__field(u8, level)
__field(int, grplo)
__field(int, grphi)
@@ -121,7 +122,7 @@ TRACE_EVENT(rcu_future_grace_period,
TP_fast_assign(
__entry->rcuname = rcuname;
__entry->gp_seq = gp_seq;
- __entry->c = c;
+ __entry->gp_seq_start = gp_seq_start;
__entry->level = level;
__entry->grplo = grplo;
__entry->grphi = grphi;
@@ -129,7 +130,7 @@ TRACE_EVENT(rcu_future_grace_period,
),

TP_printk("%s %lu %lu %u %d %d %s",
- __entry->rcuname, __entry->gp_seq, __entry->c, __entry->level,
+ __entry->rcuname, __entry->gp_seq, __entry->gp_seq_start, __entry->level,
__entry->grplo, __entry->grphi, __entry->gpevent)
);

@@ -751,7 +752,7 @@ TRACE_EVENT(rcu_barrier,
#else /* #ifdef CONFIG_RCU_TRACE */

#define trace_rcu_grace_period(rcuname, gp_seq, gpevent) do { } while (0)
-#define trace_rcu_future_grace_period(rcuname, gp_seq, c, \
+#define trace_rcu_future_grace_period(rcuname, gp_seq, gp_seq_start, \
level, grplo, grphi, event) \
do { } while (0)
#define trace_rcu_grace_period_init(rcuname, gp_seq, level, grplo, grphi, \
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 29ccc60bdbfc..9f5679ba413b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1541,13 +1541,18 @@ void rcu_cpu_stall_reset(void)

/* Trace-event wrapper function for trace_rcu_future_grace_period. */
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
- unsigned long c, const char *s)
+ unsigned long gp_seq_start, const char *s)
{
- trace_rcu_future_grace_period(rdp->rsp->name, rnp->gp_seq, c,
+ trace_rcu_future_grace_period(rdp->rsp->name, rnp->gp_seq, gp_seq_start,
rnp->level, rnp->grplo, rnp->grphi, s);
}

/*
+ * rcu_start_this_gp - Request the start of a particular grace period
+ * @rnp: The leaf node of the CPU from which to start.
+ * @rdp: The rcu_data corresponding to the CPU from which to start.
+ * @gp_seq_start: The gp_seq of the grace period to start.
+ *
* Start the specified grace period, as needed to handle newly arrived
* callbacks. The required future grace periods are recorded in each
* rcu_node structure's ->gp_seq_needed field. Returns true if there
@@ -1555,9 +1560,11 @@ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
*
* The caller must hold the specified rcu_node structure's ->lock, which
* is why the caller is responsible for waking the grace-period kthread.
+ *
+ * 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,
- unsigned long c)
+ unsigned long gp_seq_start)
{
bool ret = false;
struct rcu_state *rsp = rdp->rsp;
@@ -1573,18 +1580,19 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
* not be released.
*/
raw_lockdep_assert_held_rcu_node(rnp);
- trace_rcu_this_gp(rnp, rdp, c, TPS("Startleaf"));
+ trace_rcu_this_gp(rnp, rdp, gp_seq_start, 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, c) ||
- rcu_seq_done(&rnp_root->gp_seq, c) ||
+ if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_start) ||
+ rcu_seq_done(&rnp_root->gp_seq, gp_seq_start) ||
(rnp != rnp_root &&
rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) {
- trace_rcu_this_gp(rnp_root, rdp, c, TPS("Prestarted"));
+ trace_rcu_this_gp(rnp_root, rdp, gp_seq_start,
+ TPS("Prestarted"));
goto unlock_out;
}
- rnp_root->gp_seq_needed = c;
+ rnp_root->gp_seq_needed = gp_seq_start;
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
goto unlock_out;
if (rnp_root != rnp && rnp_root->parent != NULL)
@@ -1595,14 +1603,14 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,

/* If GP already in progress, just leave, otherwise start one. */
if (rcu_gp_in_progress(rsp)) {
- trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedleafroot"));
+ trace_rcu_this_gp(rnp_root, rdp, gp_seq_start, TPS("Startedleafroot"));
goto unlock_out;
}
- trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedroot"));
+ trace_rcu_this_gp(rnp_root, rdp, gp_seq_start, TPS("Startedroot"));
WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
rsp->gp_req_activity = jiffies;
if (!rsp->gp_kthread) {
- trace_rcu_this_gp(rnp_root, rdp, c, TPS("NoGPkthread"));
+ trace_rcu_this_gp(rnp_root, rdp, gp_seq_start, TPS("NoGPkthread"));
goto unlock_out;
}
trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq"));
@@ -1611,9 +1619,9 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
if (rnp != rnp_root)
raw_spin_unlock_rcu_node(rnp_root);
/* Push furthest requested GP to leaf node and rcu_data structure. */
- if (ULONG_CMP_GE(rnp_root->gp_seq_needed, c)) {
- rnp->gp_seq_needed = c;
- rdp->gp_seq_needed = c;
+ if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_start)) {
+ rnp->gp_seq_needed = gp_seq_start;
+ rdp->gp_seq_needed = gp_seq_start;
}
return ret;
}
@@ -1624,14 +1632,13 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
*/
static bool rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
- unsigned long c = rnp->gp_seq;
bool needmore;
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);

needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
if (!needmore)
rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
- trace_rcu_this_gp(rnp, rdp, c,
+ trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
return needmore;
}
@@ -1667,7 +1674,7 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp)
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
- unsigned long c;
+ unsigned long gp_seq_start;
bool ret = false;

raw_lockdep_assert_held_rcu_node(rnp);
@@ -1686,9 +1693,9 @@ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
* accelerating callback invocation to an earlier grace-period
* number.
*/
- c = rcu_seq_snap(&rsp->gp_seq);
- if (rcu_segcblist_accelerate(&rdp->cblist, c))
- ret = rcu_start_this_gp(rnp, rdp, c);
+ gp_seq_start = rcu_seq_snap(&rsp->gp_seq);
+ if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_start))
+ ret = rcu_start_this_gp(rnp, rdp, gp_seq_start);

/* Trace depending on how much we were able to accelerate. */
if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
--
2.17.0.441.gb46fe60e1d-goog
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