v6->v7: - Remove support for unfair lock, so only fair qrwlock will be provided. - Move qrwlock.c to the kernel/locking directory. v5->v6: - Modify queue_read_can_lock() to avoid false positive result. - Move the two slowpath functions' performance tuning change from patch 4 to patch 1. - Add a new optional patch to use the new smp_store_release() function if that is merged. v4->v5: - Fix wrong definitions for QW_MASK_FAIR & QW_MASK_UNFAIR macros. - Add an optional patch 4 which should only be applied after the mcs_spinlock.h header file is merged. v3->v4: - Optimize the fast path with better cold cache behavior and performance. - Removing some testing code. - Make x86 use queue rwlock with no user configuration. v2->v3: - Make read lock stealing the default and fair rwlock an option with a different initializer. - In queue_read_lock_slowpath(), check irq_count() and force spinning and lock stealing in interrupt context. - Unify the fair and classic read-side code path, and make write-side to use cmpxchg with 2 different writer states. This slows down the write lock fastpath to make the read side more efficient, but is still slightly faster than a spinlock. v1->v2: - Improve lock fastpath performance. - Optionally provide classic read/write lock behavior for backward compatibility. - Use xadd instead of cmpxchg for fair reader code path to make it immute to reader contention. - Run more performance testing. As mentioned in the LWN article http://lwn.net/Articles/364583/, the read/write lock suffer from an unfairness problem that it is possible for a stream of incoming readers to block a waiting writer from getting the lock for a long time. Also, a waiting reader/writer contending a rwlock in local memory will have a higher chance of acquiring the lock than a reader/writer in remote node. This patch set introduces a queue-based read/write lock implementation that can largely solve this unfairness problem. The read lock slowpath will check if the reader is in an interrupt context. If so, it will force lock spinning and stealing without waiting in a queue. This is to ensure the read lock will be granted as soon as possible. The queue write lock can also be used as a replacement for ticket spinlocks that are highly contended if lock size increase is not an issue. This patch set currently provides queue read/write lock support on x86 architecture only. Support for other architectures can be added later on once architecture specific support infrastructure is added and proper testing is done. The optional patch 3 has a dependency on the the mcs_spinlock.h header file which has not been merged yet. So this patch should only be applied after the mcs_spinlock.h header file is merged. The optional patch 4 use the new smp_store_release() and smp_load_acquire() functions which are being reviewed & not merged yet. Waiman Long (4): qrwlock: A queue read/write lock implementation qrwlock x86: Enable x86 to use queue read/write lock qrwlock: Use the mcs_spinlock helper functions for MCS queuing qrwlock: Use smp_store_release() in write_unlock() arch/x86/Kconfig | 1 + arch/x86/include/asm/spinlock.h | 2 + arch/x86/include/asm/spinlock_types.h | 4 + include/asm-generic/qrwlock.h | 200 +++++++++++++++++++++++++++++++++ kernel/Kconfig.locks | 7 + kernel/locking/Makefile | 1 + kernel/locking/qrwlock.c | 196 ++++++++++++++++++++++++++++++++ 7 files changed, 411 insertions(+), 0 deletions(-) create mode 100644 include/asm-generic/qrwlock.h create mode 100644 kernel/locking/qrwlock.c -- 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
