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rcu: Refactor rcu_barrier() empty-list handling

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This commit saves a few lines by checking first for an empty callback
list.  If the callback list is empty, then that CPU is taken care of,
regardless of its online or nocb state.  Also simplify tracing accordingly
and fold a few lines together.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-12-10 16:25:20 -08:00
parent 82980b1622
commit 0cabb47af3
2 changed files with 12 additions and 22 deletions
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9
include/trace/events/rcu.h
View File

@ -794,16 +794,15 @@ TRACE_EVENT_RCU(rcu_torture_read,
* Tracepoint for rcu_barrier() execution. The string "s" describes * Tracepoint for rcu_barrier() execution. The string "s" describes
* the rcu_barrier phase: * the rcu_barrier phase:
* "Begin": rcu_barrier() started. * "Begin": rcu_barrier() started.
* "CB": An rcu_barrier_callback() invoked a callback, not the last.
* "EarlyExit": rcu_barrier() piggybacked, thus early exit. * "EarlyExit": rcu_barrier() piggybacked, thus early exit.
* "Inc1": rcu_barrier() piggyback check counter incremented. * "Inc1": rcu_barrier() piggyback check counter incremented.
* "OfflineNoCBQ": rcu_barrier() found offline no-CBs CPU with callbacks. * "Inc2": rcu_barrier() piggyback check counter incremented.
* "OnlineQ": rcu_barrier() found online CPU with callbacks.
* "OnlineNQ": rcu_barrier() found online CPU, no callbacks.
* "IRQ": An rcu_barrier_callback() callback posted on remote CPU. * "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
* "IRQNQ": An rcu_barrier_callback() callback found no callbacks. * "IRQNQ": An rcu_barrier_callback() callback found no callbacks.
* "CB": An rcu_barrier_callback() invoked a callback, not the last.
* "LastCB": An rcu_barrier_callback() invoked the last callback. * "LastCB": An rcu_barrier_callback() invoked the last callback.
* "Inc2": rcu_barrier() piggyback check counter incremented. * "NQ": rcu_barrier() found a CPU with no callbacks.
* "OnlineQ": rcu_barrier() found online CPU with callbacks.
* The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
* is the count of remaining callbacks, and "done" is the piggybacking count. * is the count of remaining callbacks, and "done" is the piggybacking count.
*/ */

25
kernel/rcu/tree.c
View File

@ -4030,8 +4030,7 @@ void rcu_barrier(void)
/* Did someone else do our work for us? */ /* Did someone else do our work for us? */
if (rcu_seq_done(&rcu_state.barrier_sequence, s)) { if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
rcu_state.barrier_sequence);
smp_mb(); /* caller's subsequent code after above check. */ smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(&rcu_state.barrier_mutex); mutex_unlock(&rcu_state.barrier_mutex);
return; return;
@ -4059,26 +4058,18 @@ void rcu_barrier(void)
*/ */
for_each_possible_cpu(cpu) { for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu); rdp = per_cpu_ptr(&rcu_data, cpu);
if (cpu_is_offline(cpu) && if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
!rcu_rdp_is_offloaded(rdp)) rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
continue; continue;
if (rcu_segcblist_n_cbs(&rdp->cblist) && cpu_online(cpu)) { }
rcu_barrier_trace(TPS("OnlineQ"), cpu, if (cpu_online(cpu)) {
rcu_state.barrier_sequence); rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
smp_call_function_single(cpu, rcu_barrier_func, (void *)cpu, 1); smp_call_function_single(cpu, rcu_barrier_func, (void *)cpu, 1);
} else if (rcu_segcblist_n_cbs(&rdp->cblist) && } else {
cpu_is_offline(cpu)) { rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu,
rcu_state.barrier_sequence);
local_irq_disable(); local_irq_disable();
rcu_barrier_func((void *)cpu); rcu_barrier_func((void *)cpu);
local_irq_enable(); local_irq_enable();
} else if (cpu_is_offline(cpu)) {
rcu_barrier_trace(TPS("OfflineNoCBNoQ"), cpu,
rcu_state.barrier_sequence);
} else {
rcu_barrier_trace(TPS("OnlineNQ"), cpu,
rcu_state.barrier_sequence);
} }
} }
cpus_read_unlock(); cpus_read_unlock();