The existing contention_begin/contention_end tracepoints fire on the waiter side. The lock holder's identity and stack can be captured at contention_begin time (e.g. perf lock contention --lock-owner), but this reflects the holder's state when a waiter arrives, not when the lock is actually released.
This series adds a contended_release tracepoint that fires on the holder side when a lock with waiters is released. This provides: - Hold time estimation: when the holder's own acquisition was contended, its contention_end (acquisition) and contended_release can be correlated to measure how long the lock was held under contention. - The holder's stack at release time, which may differ from what perf lock contention --lock-owner captures if the holder does significant work between the waiter's arrival and the unlock. The tracepoint is placed exclusively in slowpath unlock paths, so there is no performance impact on the uncontended fast path and expected minimal impact on binary size. Based on the feedback on the RFC, here is v2 with the suggested fixes. Since there were no objections to the approach, I am dropping the RFC tag. RFC -> v2: - Add trace_contended_release_enabled() guard before waiter checks that exist only for the tracepoint (Steven Rostedt). - Rename __percpu_up_read_slowpath() to __percpu_up_read() (Peter Zijlstra). - Add extern for __percpu_up_read() (Peter Zijlstra). - Squashed tracepoint introduction and usage commits (Masami Hiramatsu). RFC: https://lore.kernel.org/all/[email protected]/ Dmitry Ilvokhin (2): locking/percpu-rwsem: Extract __percpu_up_read() locking: Add contended_release tracepoint include/linux/percpu-rwsem.h | 15 +++------------ include/trace/events/lock.h | 17 +++++++++++++++++ kernel/locking/mutex.c | 1 + kernel/locking/percpu-rwsem.c | 21 +++++++++++++++++++++ kernel/locking/rtmutex.c | 1 + kernel/locking/rwbase_rt.c | 8 +++++++- kernel/locking/rwsem.c | 9 +++++++-- kernel/locking/semaphore.c | 4 +++- 8 files changed, 60 insertions(+), 16 deletions(-) -- 2.52.0
