Re: [PATCH 5/6] locking/rwsem: Unify wait loop
From: Waiman Long
Date: Thu Feb 23 2023 - 17:47:19 EST
On 2/23/23 07:26, Peter Zijlstra wrote:
Now that the reader and writer wait loops are identical, share the
code.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/locking/rwsem.c | 117 +++++++++++++++++++------------------------------
1 file changed, 47 insertions(+), 70 deletions(-)
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -650,13 +650,11 @@ static void rwsem_mark_wake(struct rw_se
* optionally wake up waiters before it returns.
*/
static inline void
-rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
- struct wake_q_head *wake_q)
+rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
__releases(&sem->wait_lock)
{
bool first = rwsem_first_waiter(sem) == waiter;
-
- wake_q_init(wake_q);
+ DEFINE_WAKE_Q(wake_q);
/*
* If the wait_list isn't empty and the waiter to be deleted is
@@ -664,10 +662,10 @@ rwsem_del_wake_waiter(struct rw_semaphor
* be eligible to acquire or spin on the lock.
*/
if (rwsem_del_waiter(sem, waiter) && first)
- rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
+ rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
- if (!wake_q_empty(wake_q))
- wake_up_q(wake_q);
+ if (!wake_q_empty(&wake_q))
+ wake_up_q(&wake_q);
}
/*
@@ -993,6 +991,46 @@ static inline void rwsem_cond_wake_waite
rwsem_mark_wake(sem, wake_type, wake_q);
}
+#define waiter_type(_waiter, _r, _w) \
+ ((_waiter)->type == RWSEM_WAITING_FOR_READ ? (_r) : (_w))
+
+static __always_inline struct rw_semaphore *
+rwsem_waiter_wait(struct rw_semaphore *sem, struct rwsem_waiter *waiter, int state)
+{
+ trace_contention_begin(sem, waiter_type(waiter, LCB_F_READ, LCB_F_WRITE));
+
+ /* wait to be given the lock */
+ for (;;) {
+ set_current_state(state);
+ if (!smp_load_acquire(&waiter->task)) {
+ /* Matches rwsem_waiter_wake()'s smp_store_release(). */
+ break;
+ }
+ if (signal_pending_state(state, current)) {
+ raw_spin_lock_irq(&sem->wait_lock);
+ if (waiter->task)
+ goto out_nolock;
+ raw_spin_unlock_irq(&sem->wait_lock);
+ /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
+ break;
+ }
+ schedule_preempt_disabled();
+ lockevent_inc(waiter_type(waiter, rwsem_sleep_reader, rwsem_sleep_writer));
+ }
+
+ __set_current_state(TASK_RUNNING);
+ lockevent_inc(waiter_type(waiter, rwsem_rlock, rwsem_wlock));
+ trace_contention_end(sem, 0);
+ return sem;
+
+out_nolock:
+ rwsem_del_wake_waiter(sem, waiter);
+ __set_current_state(TASK_RUNNING);
Similar to boqun's comment, we should move __set_current_state() before
rwsem_del_wake_waiter().
Unfortunately, lockevent_inc() doesn't work with waiter_type() like that
as the compilation will fail if CONFIG_LOCK_EVENT_COUNTS is enabled.
Could you include the attached patch in your series and make the
following changes?
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index deb0d016a6ce..5b14b0d076fd 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1021,13 +1021,14 @@ static inline void rwsem_cond_wake_waiter(struct
rw_semaphore *sem, long count,
rwsem_mark_wake(sem, wake_type, wake_q);
}
-#define waiter_type(_waiter, _r, _w) \
- ((_waiter)->type == RWSEM_WAITING_FOR_READ ? (_r) : (_w))
+#define waiter_type(_reader, _r, _w) ((_reader) ? (_r) : (_w))
static __always_inline struct rw_semaphore *
rwsem_waiter_wait(struct rw_semaphore *sem, struct rwsem_waiter
*waiter, int state)
{
- trace_contention_begin(sem, waiter_type(waiter, LCB_F_READ,
LCB_F_WRITE));
+ bool reader = waiter->type == RWSEM_WAITING_FOR_READ;
+
+ trace_contention_begin(sem, waiter_type(reader, LCB_F_READ,
LCB_F_WRITE));
/* wait to be given the lock */
for (;;) {
@@ -1045,18 +1046,18 @@ rwsem_waiter_wait(struct rw_semaphore *sem,
struct rwsem_waiter *waiter, int sta
break;
}
schedule_preempt_disabled();
- lockevent_inc(waiter_type(waiter, rwsem_sleep_reader,
rwsem_sleep_writer));
+ lockevent_cond_inc2(reader, rwsem_sleep_reader,
rwsem_sleep_writer);
}
__set_current_state(TASK_RUNNING);
- lockevent_inc(waiter_type(waiter, rwsem_rlock, rwsem_wlock));
+ lockevent_cond_inc2(reader, rwsem_rlock, rwsem_wlock);
trace_contention_end(sem, 0);
return sem;
out_nolock:
rwsem_del_wake_waiter(sem, waiter);
__set_current_state(TASK_RUNNING);
- lockevent_inc(waiter_type(waiter, rwsem_rlock_fail,
rwsem_wlock_fail));
+ lockevent_cond_inc2(reader, rwsem_rlock_fail, rwsem_wlock_fail);
trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}
Thanks,
Longman
lockevent_inc
From 490fb153006941ec7b576c9e89cb220a0739a95c Mon Sep 17 00:00:00 2001
From: Waiman Long <longman@xxxxxxxxxx>
Date: Thu, 23 Feb 2023 17:32:06 -0500
Subject: [PATCH] locking/lock_events: Add a new lockevent_cond_inc2() helper
Add a new lockevent_cond_inc2(cond, true_event, false_event) helper
to conditionally increment one of the 2 given events.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/locking/lock_events.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
index 8c7e7d25f09c..668c2f1397f6 100644
--- a/kernel/locking/lock_events.h
+++ b/kernel/locking/lock_events.h
@@ -43,6 +43,21 @@ static inline void __lockevent_inc(enum lock_events event, bool cond)
#define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true)
#define lockevent_cond_inc(ev, c) __lockevent_inc(LOCKEVENT_ ##ev, c)
+/*
+ * Increment either the tevent (cond true) or fevent (cond false)
+ */
+static inline void __lockevent_cond_inc2(bool cond, enum lock_events tevent,
+ enum lock_events fevent)
+{
+ if (cond)
+ raw_cpu_inc(lockevents[tevent]);
+ else
+ raw_cpu_inc(lockevents[fevent]);
+
+}
+#define lockevent_cond_inc2(c, tev, fev) \
+ __lockevent_cond_inc2(c, LOCKEVENT_ ##tev, LOCKEVENT_ ##fev)
+
static inline void __lockevent_add(enum lock_events event, int inc)
{
raw_cpu_add(lockevents[event], inc);
@@ -55,6 +70,7 @@ static inline void __lockevent_add(enum lock_events event, int inc)
#define lockevent_inc(ev)
#define lockevent_add(ev, c)
#define lockevent_cond_inc(ev, c)
+#define lockevent_cond_inc2(c, tev, fev)
#endif /* CONFIG_LOCK_EVENT_COUNTS */
#endif /* __LOCKING_LOCK_EVENTS_H */
--
2.31.1