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 series is structured as follows: 1. Remove unnecessary linux/sched.h include from trace/events/lock.h. 2. Extract __percpu_up_read() out of the inline percpu_up_read() to avoid binary size increase from adding a tracepoint. 3. Add contended_release tracepoint and instrument sleepable locks: mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and rwbase_rt. 4. RFC. Extend contended_release to queued spinlocks and queued rwlocks. v2 -> v3: - Added new patch: extend contended_release tracepoint to queued spinlocks and queued rwlocks (marked as RFC, requesting feedback). This is prompted by Matthew Wilcox's suggestion to try to come up with generic instrumentation, instead of instrumenting each "special" lock manually. See [1] for the discussion. - Reworked tracepoint placement to fire before the lock is released and before the waiter is woken where possible, for consistency with spinning locks where there is no explicit wake (inspired by Usama Arif's suggestion). - Remove unnecessary linux/sched.h include from trace/events/lock.h. 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). v2: https://lore.kernel.org/all/[email protected]/ RFC: https://lore.kernel.org/all/[email protected]/ [1]: https://lore.kernel.org/all/[email protected]/ Dmitry Ilvokhin (4): tracing/lock: Remove unnecessary linux/sched.h include locking/percpu-rwsem: Extract __percpu_up_read() locking: Add contended_release tracepoint to sleepable locks locking: Add contended_release tracepoint to spinning locks include/asm-generic/qrwlock.h | 48 +++++++++++++++++++++++++++------ include/asm-generic/qspinlock.h | 25 +++++++++++++++-- include/linux/percpu-rwsem.h | 15 +++-------- include/trace/events/lock.h | 18 ++++++++++++- kernel/locking/mutex.c | 3 +++ kernel/locking/percpu-rwsem.c | 22 +++++++++++++++ kernel/locking/qrwlock.c | 16 +++++++++++ kernel/locking/qspinlock.c | 8 ++++++ kernel/locking/rtmutex.c | 1 + kernel/locking/rwbase_rt.c | 8 +++++- kernel/locking/rwsem.c | 9 +++++-- kernel/locking/semaphore.c | 4 ++- 12 files changed, 150 insertions(+), 27 deletions(-) -- 2.52.0
