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| author |   Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-06-25 15:52:50 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-17 14:58:52 -0700 |
| commit | 543c6158f6dff20a741dfa492771f18ceaa1a109 (patch) | |
| tree | 8897854acacf5f31bbd4f861a8b2f9e43dd0190d /kernel/rcu | |
| parent | rcu: Abstract sequence counting from synchronize_sched_expedited() (diff) | |
| download | linux-dev-543c6158f6dff20a741dfa492771f18ceaa1a109.tar.xz linux-dev-543c6158f6dff20a741dfa492771f18ceaa1a109.zip | |
rcu: Make synchronize_rcu_expedited() use sequence-counter scheme
Although synchronize_rcu_expedited() uses a sequence-counter scheme, it
is based on a single increment per grace period, which means that tasks
piggybacking off of concurrent grace periods may be forced to wait longer
than necessary. This commit therefore applies the new sequence-count
functions developed for synchronize_sched_expedited() to speed things
up a bit and to consolidate the sequence-counter implementation.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 16 |
1 files changed, 6 insertions, 10 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ef41c1b04ba6..759883f51de7 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -536,7 +536,6 @@ void synchronize_rcu(void) EXPORT_SYMBOL_GPL(synchronize_rcu); static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); -static unsigned long sync_rcu_preempt_exp_count; static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); /* @@ -704,12 +703,10 @@ void synchronize_rcu_expedited(void) { struct rcu_node *rnp; struct rcu_state *rsp = rcu_state_p; - unsigned long snap; + unsigned long s; int trycount = 0; - smp_mb(); /* Caller's modifications seen first by other CPUs. */ - snap = READ_ONCE(sync_rcu_preempt_exp_count) + 1; - smp_mb(); /* Above access cannot bleed into critical section. */ + s = rcu_exp_gp_seq_snap(rsp); /* * Acquire lock, falling back to synchronize_rcu() if too many @@ -717,8 +714,7 @@ void synchronize_rcu_expedited(void) * expedited grace period for us, just leave. */ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { - if (ULONG_CMP_LT(snap, - READ_ONCE(sync_rcu_preempt_exp_count))) + if (rcu_exp_gp_seq_done(rsp, s)) goto mb_ret; /* Others did our work for us. */ if (trycount++ < 10) { udelay(trycount * num_online_cpus()); @@ -727,8 +723,9 @@ void synchronize_rcu_expedited(void) return; } } - if (ULONG_CMP_LT(snap, READ_ONCE(sync_rcu_preempt_exp_count))) + if (rcu_exp_gp_seq_done(rsp, s)) goto unlock_mb_ret; /* Others did our work for us. */ + rcu_exp_gp_seq_start(rsp); /* force all RCU readers onto ->blkd_tasks lists. */ synchronize_sched_expedited(); @@ -750,8 +747,7 @@ void synchronize_rcu_expedited(void) sync_rcu_preempt_exp_done(rnp)); /* Clean up and exit. */ - smp_mb(); /* ensure expedited GP seen before counter increment. */ - WRITE_ONCE(sync_rcu_preempt_exp_count, sync_rcu_preempt_exp_count + 1); + rcu_exp_gp_seq_end(rsp); unlock_mb_ret: mutex_unlock(&sync_rcu_preempt_exp_mutex); mb_ret: |