Changes from v14: ---------------- - Change the way the main queue is scanned and reordered in cna_wait_head_or_lock(), based on Peter's suggestion. In detail: instead of inspecting only one queue node, we now scan (and move nodes into the secondary queue) as long as the lock remains busy. This simplified the code quite a bit, as we don't need to call cna_order_queue() again from cna_lock_handoff(). - Use local_clock() instead of relying on jiffies to decide when to flush the secondary queue, per Andy's suggestion. - Use module_param() for numa_spinlock_threshold_ns, so it can be tweaked at runtime, per Andy's suggestion. - Reduce the default value for numa_spinlock_threshold_ns to 1ms based on the comments from Andy and Peter. The performance numbers below include results with the new default as well as with the value of 10ms, which was the default threshold in previous revisions of the series. 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 v5.12.0, commit 3cf5c8ea3a66, compiled in the default configuration. 'CNA' is the modified kernel with NUMA_AWARE_SPINLOCKS set and the new default threshold of 1ms for flushing the secondary queue (numa_spinlock_threshold_ns); 'CNA-10ms' is the same as CNA, but uses the threshold of 10ms. The speedup is calculated by dividing the result of 'CNA' and 'CNA-10ms', respectively, by the result achieved with 'stock'. #thr stock CNA / speedup CNA-10ms / speedup 1 2.695 (0.108) 2.704 (0.099) / 1.003 2.712 (0.077) / 1.006 2 2.753 (0.187) 2.785 (0.171) / 1.012 2.822 (0.174) / 1.025 4 4.355 (0.139) 4.417 (0.179) / 1.014 4.361 (0.181) / 1.001 8 5.163 (0.119) 7.017 (0.195) / 1.359 7.369 (0.186) / 1.427 16 5.944 (0.134) 9.110 (0.242) / 1.532 9.187 (0.233) / 1.546 32 6.310 (0.082) 9.710 (0.156) / 1.539 9.827 (0.161) / 1.557 36 6.374 (0.112) 9.777 (0.141) / 1.534 9.830 (0.124) / 1.542 72 6.170 (0.139) 9.922 (0.190) / 1.608 9.945 (0.136) / 1.612 108 6.002 (0.089) 9.651 (0.176) / 1.608 9.847 (0.125) / 1.641 142 5.784 (0.079) 9.477 (0.089) / 1.638 9.641 (0.113) / 1.667 The following tables contain throughput results (ops/us) from the same setup for will-it-scale/open1_threads: #thr stock CNA / speedup CNA-10ms / speedup 1 0.503 (0.004) 0.501 (0.001) / 0.996 0.503 (0.002) / 1.000 2 0.783 (0.014) 0.773 (0.011) / 0.988 0.774 (0.016) / 0.989 4 1.422 (0.025) 1.398 (0.030) / 0.983 1.403 (0.025) / 0.987 8 1.753 (0.104) 1.641 (0.132) / 0.936 1.675 (0.134) / 0.956 16 1.851 (0.097) 1.760 (0.103) / 0.951 1.774 (0.119) / 0.959 32 0.905 (0.081) 1.708 (0.081) / 1.888 1.738 (0.069) / 1.922 36 0.895 (0.058) 1.726 (0.065) / 1.928 1.735 (0.081) / 1.938 72 0.823 (0.033) 1.610 (0.067) / 1.957 1.647 (0.067) / 2.002 108 0.845 (0.035) 1.588 (0.054) / 1.878 1.740 (0.067) / 2.058 142 0.840 (0.030) 1.546 (0.042) / 1.839 1.740 (0.048) / 2.070 and will-it-scale/lock2_threads: #thr stock CNA / speedup CNA-10ms / speedup 1 1.551 (0.003) 1.558 (0.006) / 1.005 1.558 (0.003) / 1.005 2 2.722 (0.064) 2.704 (0.063) / 0.993 2.727 (0.058) / 1.002 4 5.286 (0.178) 5.360 (0.151) / 1.014 5.360 (0.135) / 1.014 8 4.115 (0.297) 3.906 (0.383) / 0.949 4.062 (0.366) / 0.987 16 4.119 (0.121) 3.950 (0.131) / 0.959 4.009 (0.132) / 0.973 32 2.508 (0.097) 3.805 (0.106) / 1.517 3.960 (0.091) / 1.579 36 2.457 (0.101) 3.810 (0.072) / 1.551 3.931 (0.106) / 1.600 72 1.913 (0.103) 3.530 (0.070) / 1.845 3.860 (0.078) / 2.018 108 1.891 (0.109) 3.410 (0.079) / 1.803 3.881 (0.097) / 2.052 142 1.752 (0.096) 3.236 (0.080) / 1.847 3.774 (0.078) / 2.155 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 throughput results (ops/us) for the leveldb ‘readrandom’ benchmark: #thr stock CNA / speedup CNA-10ms / speedup 1 0.533 (0.011) 0.539 (0.014) / 1.012 0.536 (0.013) / 1.006 2 0.854 (0.022) 0.856 (0.017) / 1.003 0.857 (0.020) / 1.004 4 1.236 (0.028) 1.238 (0.054) / 1.002 1.217 (0.054) / 0.985 8 1.207 (0.117) 1.198 (0.122) / 0.993 1.155 (0.138) / 0.957 16 0.758 (0.055) 1.128 (0.118) / 1.489 1.068 (0.131) / 1.409 32 0.743 (0.027) 1.153 (0.028) / 1.551 1.147 (0.021) / 1.543 36 0.708 (0.027) 1.150 (0.024) / 1.623 1.137 (0.026) / 1.605 72 0.629 (0.016) 1.112 (0.019) / 1.767 1.134 (0.019) / 1.802 108 0.610 (0.012) 1.053 (0.018) / 1.725 1.130 (0.017) / 1.853 142 0.606 (0.013) 1.008 (0.020) / 1.664 1.110 (0.023) / 1.833 Further comments are welcome and appreciated. Alex Kogan (6): 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 locking/qspinlock: Introduce the shuffle reduction optimization into CNA .../admin-guide/kernel-parameters.txt | 18 + 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 | 425 ++++++++++++++++++ kernel/locking/qspinlock_paravirt.h | 2 +- 10 files changed, 562 insertions(+), 23 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.24.3 (Apple Git-128)
