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SubjectRe: [RFC PATCH 01/12] rcu: Implement rcu_segcblist_is_offloaded() config dependent
On Tue, Sep 22, 2020 at 11:43:26PM +0200, Frederic Weisbecker wrote:
> On Mon, Sep 21, 2020 at 05:27:32PM -0700, Paul E. McKenney wrote:
> > On Mon, Sep 21, 2020 at 02:43:40PM +0200, Frederic Weisbecker wrote:
> > > This simplify the usage of this API and avoid checking the kernel
> > > config from the callers.
> > >
> > > Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > > Cc: Paul E. McKenney <paulmck@kernel.org>
> > > Cc: Josh Triplett <josh@joshtriplett.org>
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > > Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> > > Cc: Joel Fernandes <joel@joelfernandes.org>
> >
> > Nice cleanup! I clearly should have done it this way to start with.
> >
> > Any reason I shouldn't pull this into -rcu right now?
>
> I think that very one can be applied indeed.

Very well! I had to hand-apply it due to recent -rcu thrash, and as
usual I could not resist wordsmithing the commit log. Please let
me know if I messed anything up.

Thanx, Paul

------------------------------------------------------------------------

commit 99a2a9b00b1f44019e5667cdbd44b8eb82e9f0a9
Author: Frederic Weisbecker <frederic@kernel.org>
Date: Mon Sep 21 14:43:40 2020 +0200

rcu: Implement rcu_segcblist_is_offloaded() config dependent

This commit simplifies the use of the rcu_segcblist_is_offloaded() API so
that its callers no longer need to check the RCU_NOCB_CPU Kconfig option.
Note that rcu_segcblist_is_offloaded() is defined in the header file,
which means that the generated code should be just as efficient as before.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 5c293af..492262b 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -62,7 +62,7 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
/* Is the specified rcu_segcblist offloaded? */
static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
{
- return rsclp->offloaded;
+ return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded;
}

/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2424e2a..6d9ec8e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1609,8 +1609,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
{
bool ret = false;
bool need_qs;
- const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_is_offloaded(&rdp->cblist);
+ const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);

raw_lockdep_assert_held_rcu_node(rnp);

@@ -2054,8 +2053,7 @@ static void rcu_gp_cleanup(void)
needgp = true;
}
/* Advance CBs to reduce false positives below. */
- offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_is_offloaded(&rdp->cblist);
+ offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
@@ -2254,8 +2252,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
unsigned long flags;
unsigned long mask;
bool needwake = false;
- const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_is_offloaded(&rdp->cblist);
+ const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
struct rcu_node *rnp;

WARN_ON_ONCE(rdp->cpu != smp_processor_id());
@@ -2423,8 +2420,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
{
int div;
unsigned long flags;
- const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_is_offloaded(&rdp->cblist);
+ const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count;
@@ -2681,8 +2677,7 @@ static __latent_entropy void rcu_core(void)
unsigned long flags;
struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
- const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_is_offloaded(&rdp->cblist);
+ const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);

if (cpu_is_offline(smp_processor_id()))
return;
@@ -2984,8 +2979,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
rcu_segcblist_n_cbs(&rdp->cblist));

/* Go handle any RCU core processing required. */
- if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
+ if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
} else {
__call_rcu_core(rdp, head, flags);
@@ -3739,8 +3733,7 @@ static int rcu_pending(int user)

/* Has RCU gone idle with this CPU needing another grace period? */
if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
- (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) ||
- !rcu_segcblist_is_offloaded(&rdp->cblist)) &&
+ !rcu_segcblist_is_offloaded(&rdp->cblist) &&
!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return 1;

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