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 classic 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 while, at the same time, can optionally provide the classic read/write lock behavior for those locks that need it. This new queue read/write lock is both fairer than the classic read/write lock and will be faster in lock contention situations. 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. There is no change in the interface. By just selecting the QUEUE_RWLOCK config parameter during the configuration phase, the classic read/write lock will be replaced by the new queue read/write lock. This will made the systems more deterministic and faster in lock contention situations. In uncontended cases, the queue read/write lock may be a bit slower than the classic one depending on the exact mix of read and write locking primitives. Given the fact that locking overhead is typically a very small percentage of the total CPU time in uncontended cases, there won't be any noticeable degraduation in performance with this replacement. This patch set currently provides queue read/write lock support on x86 architecture only. Support for other architectures can be added later on once proper testing is done. Signed-off-by: Waiman Long <Waiman.Long@xxxxxx> Waiman Long (3): qrwlock: A queue read/write lock implementation qrwlock x86: Enable x86 to use queue read/write lock qrwlock: Optionally enable classic read/write lock behavior arch/x86/Kconfig | 3 + arch/x86/include/asm/spinlock.h | 2 + arch/x86/include/asm/spinlock_types.h | 4 + include/asm-generic/qrwlock.h | 251 +++++++++++++++++++++++++++++++++ include/linux/rwlock.h | 15 ++ include/linux/rwlock_types.h | 12 ++- include/linux/spinlock_types.h | 4 + lib/Kconfig | 23 +++ lib/Makefile | 1 + lib/qrwlock.c | 194 +++++++++++++++++++++++++ lib/spinlock_debug.c | 20 +++ 11 files changed, 528 insertions(+), 1 deletions(-) create mode 100644 include/asm-generic/qrwlock.h create mode 100644 lib/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
