From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, john.p.donnelly@oracle.com,
"Hillf Danton" <hdanton@sina.com>,
"Mukesh Ojha" <quic_mojha@quicinc.com>,
"Ting11 Wang 王婷" <wangting11@xiaomi.com>,
"Waiman Long" <longman@redhat.com>
Subject: [PATCH v3 5/5] locking/rwsem: Update handoff lock events tracking
Date: Mon, 17 Oct 2022 17:13:56 -0400 [thread overview]
Message-ID: <20221017211356.333862-6-longman@redhat.com> (raw)
In-Reply-To: <20221017211356.333862-1-longman@redhat.com>
With the new direct rwsem lock handoff, the corresponding handoff lock
events are updated to also track the number of secondary lock handoffs
in rwsem_down_read_slowpath() to see how prevalent those handoff
events are. The number of primary lock handoffs in the unlock paths is
(rwsem_handoff_read + rwsem_handoff_write - rwsem_handoff_rslow).
After running a 96-thread rwsem microbenchmark with equal number
of readers and writers on a 2-socket 96-thread system for 40s, the
following handoff stats were obtained:
rwsem_handoff_read=189
rwsem_handoff_rslow=1
rwsem_handoff_write=6678
rwsem_handoff_wspin=6681
The number of primary handoffs was 6866, whereas there was only one
secondary handoff for this test run.
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/lock_events_list.h | 6 ++++--
kernel/locking/rwsem.c | 9 +++++----
2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h
index 97fb6f3f840a..04d101767c2c 100644
--- a/kernel/locking/lock_events_list.h
+++ b/kernel/locking/lock_events_list.h
@@ -63,7 +63,9 @@ LOCK_EVENT(rwsem_rlock) /* # of read locks acquired */
LOCK_EVENT(rwsem_rlock_steal) /* # of read locks by lock stealing */
LOCK_EVENT(rwsem_rlock_fast) /* # of fast read locks acquired */
LOCK_EVENT(rwsem_rlock_fail) /* # of failed read lock acquisitions */
-LOCK_EVENT(rwsem_rlock_handoff) /* # of read lock handoffs */
LOCK_EVENT(rwsem_wlock) /* # of write locks acquired */
LOCK_EVENT(rwsem_wlock_fail) /* # of failed write lock acquisitions */
-LOCK_EVENT(rwsem_wlock_handoff) /* # of write lock handoffs */
+LOCK_EVENT(rwsem_handoff_read) /* # of read lock handoffs */
+LOCK_EVENT(rwsem_handoff_write) /* # of write lock handoffs */
+LOCK_EVENT(rwsem_handoff_rslow) /* # of handoffs in read slowpath */
+LOCK_EVENT(rwsem_handoff_wspin) /* # of handoff spins in write slowpath */
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 287606aee0e6..46aea1994bf8 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -472,10 +472,8 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
* force the issue.
*/
if (time_after(jiffies, waiter->timeout)) {
- if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
+ if (!(oldcount & RWSEM_FLAG_HANDOFF))
adjustment -= RWSEM_FLAG_HANDOFF;
- lockevent_inc(rwsem_rlock_handoff);
- }
WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED);
}
@@ -680,7 +678,6 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
*/
if (new & RWSEM_FLAG_HANDOFF) {
WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED);
- lockevent_inc(rwsem_wlock_handoff);
return false;
}
@@ -1019,10 +1016,12 @@ static void rwsem_handoff(struct rw_semaphore *sem, long adj,
wake_type = RWSEM_WAKE_ANY;
adj += RWSEM_WRITER_LOCKED;
atomic_long_set(&sem->owner, (long)waiter->task);
+ lockevent_inc(rwsem_handoff_write);
} else {
wake_type = RWSEM_WAKE_READ_OWNED;
adj += RWSEM_READER_BIAS;
__rwsem_set_reader_owned(sem, waiter->task);
+ lockevent_inc(rwsem_handoff_read);
}
atomic_long_add(adj, &sem->count);
rwsem_mark_wake(sem, wake_type, wake_q);
@@ -1128,6 +1127,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
if (rwsem_first_waiter(sem)->type == RWSEM_WAITING_FOR_READ)
adjustment = 0;
rwsem_handoff(sem, adjustment, &wake_q);
+ lockevent_inc(rwsem_handoff_rslow);
if (!adjustment) {
raw_spin_unlock_irq(&sem->wait_lock);
@@ -1257,6 +1257,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
preempt_disable();
rwsem_spin_on_owner(sem);
preempt_enable();
+ lockevent_inc(rwsem_handoff_wspin);
}
if (READ_ONCE(waiter.handoff_state) == HANDOFF_GRANTED)
goto skip_sleep;
--
2.31.1
next prev parent reply other threads:[~2022-10-17 21:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 21:13 [PATCH v3 0/5] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff Waiman Long
2022-10-17 21:13 ` [PATCH v3 1/5] locking/rwsem: Prevent non-first waiter from spinning in down_write() slowpath Waiman Long
2022-10-24 13:17 ` Peter Zijlstra
2022-10-24 13:50 ` Waiman Long
2022-10-17 21:13 ` [PATCH v3 2/5] locking/rwsem: Limit # of null owner retries for handoff writer Waiman Long
2022-10-24 13:31 ` Peter Zijlstra
2022-10-24 15:55 ` Waiman Long
2022-10-25 11:22 ` Peter Zijlstra
2022-10-25 11:48 ` Peter Zijlstra
2022-10-25 19:55 ` Waiman Long
2022-10-25 20:14 ` Peter Zijlstra
2022-10-26 1:44 ` Waiman Long
[not found] ` <20221025145843.2953-1-hdanton@sina.com>
2022-10-25 19:00 ` Waiman Long
2022-10-17 21:13 ` [PATCH v3 3/5] locking/rwsem: Change waiter->hanodff_set to a handoff_state enum Waiman Long
2022-10-17 21:13 ` [PATCH v3 4/5] locking/rwsem: Enable direct rwsem lock handoff Waiman Long
2022-10-17 21:13 ` Waiman Long [this message]
[not found] ` <20221018111424.1007-1-hdanton@sina.com>
2022-10-18 14:13 ` Mukesh Ojha
2022-10-18 17:37 ` Waiman Long
[not found] ` <20221018235138.1088-1-hdanton@sina.com>
2022-10-19 0:39 ` Waiman Long
[not found] ` <20221019022934.1166-1-hdanton@sina.com>
2022-10-19 2:49 ` Waiman Long
[not found] ` <20221019070559.1220-1-hdanton@sina.com>
2022-10-19 15:02 ` Waiman Long
2022-10-24 16:18 ` Waiman Long
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