Changes from v10: ---------------- - Revise the scan function to move waiters into the secondary queue one at a time. This way, the worst case complexity of cna_order_queue() decreases from O(n) down to O(1), as we always “scan" only one waiter. - Make the decision on when to flush the secondary queue and force lock transition to a waiter on a different NUMA node to be timer-based rather than a counter-based one, as suggested in a patch povided by Longman. - Make prioritized waiters to inherit the NUMA node id of the primary queue, to maintain the preference even if the prioritized waiter is on a different node. This is based on the patch provided by Longman. The relative performance numbers with the revised series (included below) have not changed much. 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 is enabled through a configuration option (NUMA_AWARE_SPINLOCKS). CNA is a NUMA-aware version of the MCS lock. Spinning threads are organized in two queues, a primary 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. After acquiring the MCS lock and before acquiring the spinlock, the MCS lock holder checks whether the next waiter in the primary queue (if exists) is running on the same NUMA node. If it is not, that waiter is detached from the main queue and moved into the tail of the secondary queue. This way, we gradually filter the primary queue, leaving only waiters running on the same preferred NUMA node. Note that certain priortized waiters (e.g., in irq and nmi contexts) are excluded from being moved to the secondary queue. We change the NUMA node preference after a waiter at the head of the secondary queue spins for a certain amount of time. We do that by flushing the secondary queue into the head of the primary queue, effectively changing the preference to the NUMA node of the waiter at the head of the secondary queue at the time of the flush. 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 is about 3% from the average. The 'stock' kernel is v5.9.0-rc4, commit f4d51dffc6c0, compiled in the default configuration. 'patch-CNA' is the modified kernel with NUMA_AWARE_SPINLOCKS set; the speedup is calculated dividing 'patch-CNA' by 'stock'. #thr stock patch-CNA speedup (patch-CNA/stock) 1 2.682 (0.100) 2.695 (0.075) 1.005 2 2.810 (0.155) 2.797 (0.145) 0.995 4 4.273 (0.134) 4.294 (0.159) 1.005 8 5.071 (0.108) 6.755 (0.198) 1.332 16 5.840 (0.125) 8.940 (0.188) 1.531 32 6.246 (0.113) 9.866 (0.220) 1.580 36 6.355 (0.096) 9.968 (0.215) 1.569 72 6.129 (0.116) 10.231 (0.210) 1.669 108 5.921 (0.084) 10.246 (0.208) 1.731 142 5.763 (0.089) 10.186 (0.238) 1.768 The following tables contain throughput results (ops/us) from the same setup for will-it-scale/open1_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 0.498 (0.003) 0.513 (0.001) 1.029 2 0.793 (0.014) 0.803 (0.017) 1.012 4 1.429 (0.027) 1.455 (0.027) 1.019 8 1.667 (0.089) 1.687 (0.132) 1.012 16 1.785 (0.047) 1.716 (0.068) 0.961 32 1.000 (0.064) 1.738 (0.107) 1.737 36 0.934 (0.073) 1.744 (0.076) 1.867 72 0.823 (0.043) 1.651 (0.071) 2.007 108 0.821 (0.031) 1.695 (0.063) 2.065 142 0.787 (0.027) 1.723 (0.069) 2.190 and will-it-scale/lock2_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 1.600 (0.002) 1.614 (0.004) 1.009 2 2.792 (0.066) 2.813 (0.060) 1.007 4 5.395 (0.379) 5.210 (0.500) 0.966 8 4.285 (0.278) 4.125 (0.413) 0.963 16 4.168 (0.134) 3.960 (0.146) 0.950 32 2.450 (0.106) 3.999 (0.141) 1.632 36 2.403 (0.106) 3.922 (0.106) 1.632 72 1.842 (0.098) 3.913 (0.091) 2.124 108 1.888 (0.116) 3.937 (0.074) 2.085 142 1.806 (0.113) 3.894 (0.107) 2.156 Our evaluation shows that CNA also improves performance of user applications that have hot pthread mutexes. Those mutexes are blocking, and waiting threads park and unpark via the futex mechanism in the kernel. Given that kernel futex chains, which are hashed by the mutex address, are each protected by a chain-specific spin lock, the contention on a user-mode mutex translates into contention on a kernel level spinlock. Here are the results for the leveldb ‘readrandom’ benchmark: #thr stock patch-CNA speedup (patch-CNA/stock) 1 0.529 (0.023) 0.525 (0.029) 0.993 2 0.829 (0.045) 0.847 (0.036) 1.021 4 1.122 (0.112) 1.144 (0.132) 1.020 8 1.126 (0.145) 1.124 (0.186) 0.998 16 1.029 (0.145) 1.207 (0.024) 1.173 32 0.721 (0.037) 1.158 (0.026) 1.605 36 0.690 (0.043) 1.159 (0.028) 1.680 72 0.622 (0.016) 1.136 (0.020) 1.826 108 0.608 (0.013) 1.144 (0.017) 1.882 142 0.602 (0.014) 1.122 (0.020) 1.864 Further comments are welcome and appreciated. Alex Kogan (5): locking/qspinlock: Rename mcs lock/unlock macros and make them 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: Avoid moving certain threads between waiting queues in CNA .../admin-guide/kernel-parameters.txt | 19 + arch/arm/include/asm/mcs_spinlock.h | 6 +- arch/x86/Kconfig | 20 + arch/x86/include/asm/qspinlock.h | 4 + arch/x86/kernel/alternative.c | 4 + include/asm-generic/mcs_spinlock.h | 4 +- kernel/locking/mcs_spinlock.h | 20 +- kernel/locking/qspinlock.c | 82 +++- kernel/locking/qspinlock_cna.h | 421 ++++++++++++++++++ kernel/locking/qspinlock_paravirt.h | 2 +- 10 files changed, 559 insertions(+), 23 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.21.1 (Apple Git-122.3)
