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| author | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-05-21 13:03:49 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-08-13 14:35:49 -0700 |
| commit | ec5ef87bac820be8ae9cc0a95108cded039ed8ef (patch) | |
| tree | c3159cdedc58dd861fe86ce7769e3fe2147b7f56 /kernel/rcu/tree.c | |
| parent | 4f9c1bc727f917c8c32ee1decc88e89057e0dffc (diff) | |
| download | lwn-ec5ef87bac820be8ae9cc0a95108cded039ed8ef.tar.gz lwn-ec5ef87bac820be8ae9cc0a95108cded039ed8ef.zip | |
rcu/nocb: Use build-time no-CBs check in rcu_do_batch()
Currently, rcu_do_batch() invokes rcu_segcblist_is_offloaded() each time
it needs to know whether the current CPU is a no-CBs CPU. Given that it
is not possible to change the no-CBs status of a CPU after boot, and given
that it is not possible to even have no-CBs CPUs in CONFIG_RCU_NOCB_CPU=n
kernels, this per-callback invocation wastes CPU. This commit therefore
created a const on-stack variable to allow this check to be done only
once per rcu_do_batch() invocation.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e5f30b364276..16dabd6b36d7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2087,6 +2087,8 @@ int rcutree_dead_cpu(unsigned int cpu) static void rcu_do_batch(struct rcu_data *rdp) { unsigned long flags; + const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && + rcu_segcblist_is_offloaded(&rdp->cblist); struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); long bl, count; @@ -2128,12 +2130,11 @@ static void rcu_do_batch(struct rcu_data *rdp) * Stop only if limit reached and CPU has something to do. * Note: The rcl structure counts down from zero. */ - if (-rcl.len >= bl && - !rcu_segcblist_is_offloaded(&rdp->cblist) && + if (-rcl.len >= bl && !offloaded && (need_resched() || (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) break; - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (offloaded) { WARN_ON_ONCE(in_serving_softirq()); local_bh_enable(); lockdep_assert_irqs_enabled(); @@ -2175,8 +2176,7 @@ static void rcu_do_batch(struct rcu_data *rdp) rcu_nocb_unlock_irqrestore(rdp, flags); /* Re-invoke RCU core processing if there are callbacks remaining. */ - if (!rcu_segcblist_is_offloaded(&rdp->cblist) && - rcu_segcblist_ready_cbs(&rdp->cblist)) + if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist)) invoke_rcu_core(); } |