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The following commit(s) were added to refs/heads/master by this push:
new b990d5c5 Add flag for parking lot no signal when no waiter, the
default is false (#3079)
b990d5c5 is described below
commit b990d5c5c5ea7f8bdca8de72cddce9d2ebed6938
Author: Bright Chen <[email protected]>
AuthorDate: Mon Sep 1 20:46:02 2025 +0800
Add flag for parking lot no signal when no waiter, the default is false
(#3079)
---
src/bthread/parking_lot.h | 21 +++++++++++++++++----
src/bthread/task_control.cpp | 4 +++-
2 files changed, 20 insertions(+), 5 deletions(-)
diff --git a/src/bthread/parking_lot.h b/src/bthread/parking_lot.h
index 315e9956..bbc9a7c3 100644
--- a/src/bthread/parking_lot.h
+++ b/src/bthread/parking_lot.h
@@ -22,11 +22,14 @@
#ifndef BTHREAD_PARKING_LOT_H
#define BTHREAD_PARKING_LOT_H
+#include <gflags/gflags.h>
#include "butil/atomicops.h"
#include "bthread/sys_futex.h"
namespace bthread {
+DECLARE_bool(parking_lot_no_signal_when_no_waiter);
+
// Park idle workers.
class BAIDU_CACHELINE_ALIGNMENT ParkingLot {
public:
@@ -40,13 +43,15 @@ public:
int val;
};
- ParkingLot() : _pending_signal(0), _waiter_num(0) {}
+ ParkingLot()
+ : _pending_signal(0), _waiter_num(0)
+ ,
_no_signal_when_no_waiter(FLAGS_parking_lot_no_signal_when_no_waiter) {}
// Wake up at most `num_task' workers.
// Returns #workers woken up.
int signal(int num_task) {
_pending_signal.fetch_add((num_task << 1),
butil::memory_order_release);
- if (_waiter_num.load(butil::memory_order_relaxed) == 0) {
+ if (_no_signal_when_no_waiter &&
_waiter_num.load(butil::memory_order_relaxed) == 0) {
return 0;
}
return futex_wake_private(&_pending_signal, num_task);
@@ -64,9 +69,13 @@ public:
// Fast path, no need to futex_wait.
return;
}
- _waiter_num.fetch_add(1, butil::memory_order_relaxed);
+ if (_no_signal_when_no_waiter) {
+ _waiter_num.fetch_add(1, butil::memory_order_relaxed);
+ }
futex_wait_private(&_pending_signal, expected_state.val, NULL);
- _waiter_num.fetch_sub(1, butil::memory_order_relaxed);
+ if (_no_signal_when_no_waiter) {
+ _waiter_num.fetch_sub(1, butil::memory_order_relaxed);
+ }
}
// Wakeup suspended wait() and make them unwaitable ever.
@@ -79,6 +88,10 @@ private:
// higher 31 bits for signalling, LSB for stopping.
butil::atomic<int> _pending_signal;
butil::atomic<int> _waiter_num;
+ // Whether to signal when there is no waiter.
+ // In busy worker scenarios, signal overhead
+ // can be reduced.
+ bool _no_signal_when_no_waiter;
};
} // namespace bthread
diff --git a/src/bthread/task_control.cpp b/src/bthread/task_control.cpp
index 7d121349..0b34955b 100644
--- a/src/bthread/task_control.cpp
+++ b/src/bthread/task_control.cpp
@@ -45,6 +45,9 @@ DEFINE_bool(task_group_set_worker_name, true,
namespace bthread {
+DEFINE_bool(parking_lot_no_signal_when_no_waiter, false,
+ "ParkingLot doesn't signal when there is no waiter. "
+ "In busy worker scenarios, signal overhead can be reduced.");
DEFINE_bool(enable_bthread_priority_queue, false, "Whether to enable priority
queue");
DECLARE_int32(bthread_concurrency);
@@ -189,7 +192,6 @@ TaskControl::TaskControl()
, _signal_per_second(&_cumulated_signal_count)
, _status(print_rq_sizes_in_the_tc, this)
, _nbthreads("bthread_count")
- , _enable_priority_queue(FLAGS_enable_bthread_priority_queue)
, _priority_queues(FLAGS_task_group_ntags)
, _pl_num_of_each_tag(FLAGS_bthread_parking_lot_of_each_tag)
, _tagged_pl(FLAGS_task_group_ntags)
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