This version addresses feedback from Peter and Waiman. In particular, the CNA functionality has been moved to a separate file, and is controlled by a config option (enabled by default if NUMA is enabled). An optimization has been introduced to reduce the overhead of shuffling threads between waiting queues when the lock is only lightly contended. Summary ------- Lock throughput can be increased by handing a lock to a waiter on the same NUMA node as the lock holder, provided care is taken to avoid starvation of waiters on other NUMA nodes. This patch introduces CNA (compact NUMA-aware lock) as the slow path for qspinlock. It can be enabled through a configuration option (NUMA_AWARE_SPINLOCKS). CNA is a NUMA-aware version of the MCS spin-lock. Spinning threads are organized in two queues, a main queue for threads running on the same node as the current lock holder, and a secondary queue for threads running on other nodes. Threads store the ID of the node on which they are running in their queue nodes. At the unlock time, the lock holder scans the main queue looking for a thread running on the same node. If found (call it thread T), all threads in the main queue between the current lock holder and T are moved to the end of the secondary queue, and the lock is passed to T. If such T is not found, the lock is passed to the first node in the secondary queue. Finally, if the secondary queue is empty, the lock is passed to the next thread in the main queue. To avoid starvation of threads in the secondary queue, those threads are moved back to the head of the main queue after a certain expected number of intra-node lock hand-offs. More details are available at https://arxiv.org/abs/1810.05600. We have done some performance evaluation with the locktorture module as well as with several benchmarks from the will-it-scale repo. The following locktorture results are from an Oracle X5-4 server (four Intel Xeon E7-8895 v3 @ 2.60GHz sockets with 18 hyperthreaded cores each). Each number represents an average (over 25 runs) of the total number of ops (x10^7) reported at the end of each run. The standard deviation is also reported in (), and in general, with a few exceptions, is about 3%. The 'stock' kernel is v5.0-rc8, commit 28d49e282665 ("locking/lockdep: Shrink struct lock_class_key"), compiled in the default configuration. 'patch' is the modified kernel compiled with NUMA_AWARE_SPINLOCKS not set; it is included to show that any performance changes to the existing qspinlock implementation are essentially noise. 'patch-CNA' is the modified kernel with NUMA_AWARE_SPINLOCKS set; the speedup is calculated dividing 'patch-CNA' by 'stock'. #thr stock patch patch-CNA speedup (patch-CNA/stock) 1 2.731 (0.102) 2.732 (0.093) 2.716 (0.082) 0.995 2 3.071 (0.124) 3.084 (0.109) 3.079 (0.113) 1.003 4 4.221 (0.138) 4.229 (0.087) 4.408 (0.103) 1.044 8 5.366 (0.154) 5.274 (0.094) 6.958 (0.233) 1.297 16 6.673 (0.164) 6.689 (0.095) 8.547 (0.145) 1.281 32 7.365 (0.177) 7.353 (0.183) 9.305 (0.202) 1.263 36 7.473 (0.198) 7.422 (0.181) 9.441 (0.196) 1.263 72 6.805 (0.182) 6.699 (0.170) 10.020 (0.218) 1.472 108 6.509 (0.082) 6.480 (0.115) 10.027 (0.194) 1.540 142 6.223 (0.109) 6.294 (0.100) 9.874 (0.183) 1.587 The following tables contain throughput results (ops/us) from the same setup for will-it-scale/open1_threads: #thr stock patch patch-CNA speedup (patch-CNA/stock) 1 0.565 (0.004) 0.567 (0.001) 0.565 (0.003) 0.999 2 0.892 (0.021) 0.899 (0.022) 0.900 (0.018) 1.009 4 1.503 (0.031) 1.527 (0.038) 1.481 (0.025) 0.985 8 1.755 (0.105) 1.714 (0.079) 1.683 (0.106) 0.959 16 1.740 (0.095) 1.752 (0.087) 1.693 (0.098) 0.973 32 0.884 (0.080) 0.908 (0.090) 1.686 (0.092) 1.906 36 0.907 (0.095) 0.894 (0.088) 1.709 (0.081) 1.885 72 0.856 (0.041) 0.858 (0.043) 1.707 (0.082) 1.994 108 0.858 (0.039) 0.869 (0.037) 1.732 (0.076) 2.020 142 0.809 (0.044) 0.854 (0.044) 1.728 (0.083) 2.135 and will-it-scale/lock2_threads: #thr stock patch patch-CNA speedup (patch-CNA/stock) 1 1.713 (0.004) 1.715 (0.004) 1.711 (0.004) 0.999 2 2.889 (0.057) 2.864 (0.078) 2.876 (0.066) 0.995 4 4.582 (1.032) 5.066 (0.787) 4.725 (0.959) 1.031 8 4.227 (0.196) 4.104 (0.274) 4.092 (0.365) 0.968 16 4.108 (0.141) 4.057 (0.138) 4.010 (0.168) 0.976 32 2.674 (0.125) 2.625 (0.171) 3.958 (0.156) 1.480 36 2.622 (0.107) 2.553 (0.150) 3.978 (0.116) 1.517 72 2.009 (0.090) 1.998 (0.092) 3.932 (0.114) 1.957 108 2.154 (0.069) 2.089 (0.090) 3.870 (0.081) 1.797 142 1.953 (0.106) 1.943 (0.111) 3.853 (0.100) 1.973 Further comments are welcome and appreciated. Alex Kogan (5): locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic locking/qspinlock: Refactor the qspinlock slow path locking/qspinlock: Introduce CNA into the slow path of qspinlock locking/qspinlock: Introduce starvation avoidance into CNA locking/qspinlock: Introduce the shuffle reduction optimization into CNA arch/arm/include/asm/mcs_spinlock.h | 4 +- arch/x86/Kconfig | 14 ++ include/asm-generic/qspinlock_types.h | 13 ++ kernel/locking/mcs_spinlock.h | 16 ++- kernel/locking/qspinlock.c | 77 +++++++++-- kernel/locking/qspinlock_cna.h | 245 ++++++++++++++++++++++++++++++++++ 6 files changed, 354 insertions(+), 15 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.11.0 (Apple Git-81)
