Messages in this thread | | | From | Waiman Long <> | Subject | [PATCH 0/5] locking/rwsem: Rework reader optimistic spinning | Date | Tue, 17 Nov 2020 22:04:24 -0500 |
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A recent report of SAP certification failure caused by increased system time due to rwsem reader optimistic spinning led me to reexamine the code to see the pro and cons of doing it. This led me to discover a potential lock starvation scenario as explained in patch 2. That patch does reduce reader spinning to avoid this potential problem. Patches 3 and 4 are further optimizations of the current code.
Then there is the issue of reader fragmentation that can potentially reduce performance in some heavy contention cases. Two different approaches are attempted: 1) further reduce reader optimistic spinning 2) disable reader spinning
See the performance shown in patch 5.
This patch series adopts the second approach by dropping reader spinning for now. We can discuss if this is the right move or we should try the alternative or just don't do anything further.
Waiman Long (5): locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath() locking/rwsem: Prevent potential lock starvation locking/rwsem: Enable reader optimistic lock stealing locking/rwsem: Wake up all waiting readers if RWSEM_WAKE_READ_OWNED locking/rwsem: Remove reader optimistic spinning
kernel/locking/lock_events_list.h | 6 +- kernel/locking/rwsem.c | 277 ++++++++---------------------- 2 files changed, 73 insertions(+), 210 deletions(-)
-- 2.18.1
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