Commit-ID: ec4eaccef4af28376345554580606a43d7392ed8 Gitweb: https://git.kernel.org/tip/ec4eaccef4af28376345554580606a43d7392ed8 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Sun, 22 Apr 2018 08:49:24 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Tue, 15 May 2018 10:29:51 -0700 rcu: Make rcu_migrate_callbacks wake GP kthread when needed The rcu_migrate_callbacks() function invokes rcu_advance_cbs() twice, ignoring the return value. This is OK at pressent because of failsafe code that does the wakeup when needed. However, this failsafe code acquires the root rcu_node structure's lock frequently, while rcu_migrate_callbacks() does so only once per CPU-offline operation. This commit therefore makes rcu_migrate_callbacks() wake up the RCU GP kthread when either call to rcu_advance_cbs() returns true, thus removing need for the failsafe code. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Tested-by: Nicholas Piggin <npiggin@xxxxxxxxx> --- kernel/rcu/tree.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 6ef1f2b4a6d3..f75eb5174021 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3876,6 +3876,7 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp) struct rcu_data *my_rdp; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); + bool needwake; if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist)) return; /* No callbacks to migrate. */ @@ -3887,12 +3888,15 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp) return; } raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ - rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */ - rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */ + /* Leverage recent GPs and set GP for new callbacks. */ + needwake = rcu_advance_cbs(rsp, rnp_root, rdp) || + rcu_advance_cbs(rsp, rnp_root, my_rdp); rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist); WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags); + if (needwake) + rcu_gp_kthread_wake(rsp); WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 || !rcu_segcblist_empty(&rdp->cblist), "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n", -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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