v1->v2: - Fixed a 0day build error. - Add a new patch 1 to make osq_lock() a proper acquire memory barrier. - Replaced the explicit enabling of reader spinning by an autotuning mechanism that disable reader spinning for those rwsems that may not benefit from reader spinning. - Remove the last xfs patch as it is no longer necessary. This patchset enables more aggressive optimistic spinning on both readers and writers waiting on a writer or reader owned lock. Spinning on writer is done by looking at the on_cpu flag of the lock owner. Spinning on readers, on the other hand, is count-based as there is no easy way to figure out if all the readers are running. The spinner will stop spinning once the count goes to 0. Because of that, spinning on readers may hurt performance in some cases. An autotuning mechanism is used to determine if a rwsem can benefit from reader optimistic spinning. Patch 1 updates the osq_lock() function to make it a proper acquire memory barrier. Patch 2 reduces the length of the blocking window after a read locking attempt where writer lock stealing is disabled because of the active read lock. It can improve rwsem performance for contended lock. It is independent of the rest of the patchset. Patch 3 puts in place the autotuning mechanism to check if reader optimistic spinning should be used or not. Patch 4 moves down the rwsem_down_read_failed() function for later patches. Patch 5 changes RWSEM_WAITING_BIAS to simpify reader trylock code. Patch 6 enables readers to do optimistic spinning. Waiman Long (6): locking/osq: Make lock/unlock proper acquire/release barrier locking/rwsem: Stop active read lock ASAP locking/rwsem: Enable count-based spinning on reader locking/rwsem: move down rwsem_down_read_failed function locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation locking/rwsem: Enable spinning readers arch/alpha/include/asm/rwsem.h | 7 +- arch/ia64/include/asm/rwsem.h | 6 +- arch/s390/include/asm/rwsem.h | 6 +- arch/x86/include/asm/rwsem.h | 13 ++- include/asm-generic/rwsem.h | 9 +- include/linux/rwsem.h | 19 +++- kernel/locking/osq_lock.c | 4 +- kernel/locking/rwsem-xadd.c | 238 ++++++++++++++++++++++++++++------------ 8 files changed, 209 insertions(+), 93 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
