Changes from v9: ---------------- - Revise the series based on Peter's version, adopting names, style, etc. - Add a new patch that allows to prioritize certain threads (e.g., in irq and nmi contexts) and avoids moving them between waiting queues, based on the suggestion by Longman. - Drop the shuffle reduction optimization from the series (new performance data did not justify it). - Do not call cna_init_nodes() as an early_initcall (call it from cna_configure_spin_lock_slowpath() instead), based on the comment from Longman. 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 lock holder scans the primary queue looking for a thread running on the same node (pre-scan). If found (call it thread T), all threads in the primary queue between the current lock holder and T are moved to the end of the secondary queue. If such T is not found, we make another scan of the primary queue after acquiring the spinlock when unlocking the MCS lock (post-scan), starting at the node where pre-scan stopped. If both scans fail to find such T, the MCS lock is passed to the first thread in the secondary queue. If the secondary queue is empty, the MCS lock is passed to the next thread in the primary queue. To avoid starvation of threads in the secondary queue, those threads are moved back to the head of the primary queue after a certain number of intra-node lock hand-offs. Lastly, certain threads (e.g., in in irq and nmi contexts) are given a preferential treatment -- the scan stops when such a thread is found, effectively never moving those threads into the secondary queue. 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 v5.6.0-rc6, commit 5ad0ec0b8652, 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 2.702 (0.100) 2.712 (0.122) 1.003 2 3.691 (0.162) 3.672 (0.138) 0.995 4 4.285 (0.108) 4.256 (0.124) 0.993 8 5.117 (0.133) 5.972 (0.258) 1.167 16 6.273 (0.196) 7.628 (0.274) 1.216 32 6.757 (0.122) 8.544 (0.225) 1.264 36 6.761 (0.091) 8.691 (0.170) 1.285 72 6.569 (0.132) 9.280 (0.225) 1.413 108 6.167 (0.112) 9.410 (0.171) 1.526 142 5.901 (0.117) 9.415 (0.211) 1.595 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 0.511 (0.002) 0.525 (0.003) 1.027 2 0.774 (0.018) 0.769 (0.017) 0.993 4 1.352 (0.023) 1.372 (0.032) 1.014 8 1.675 (0.090) 1.660 (0.136) 0.991 16 1.665 (0.114) 1.583 (0.092) 0.951 32 0.966 (0.038) 1.637 (0.087) 1.694 36 0.973 (0.066) 1.570 (0.081) 1.613 72 0.844 (0.040) 1.620 (0.091) 1.919 108 0.836 (0.040) 1.670 (0.084) 1.999 142 0.799 (0.043) 1.699 (0.087) 2.127 and will-it-scale/lock2_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 1.581 (0.004) 1.576 (0.007) 0.997 2 2.699 (0.059) 2.687 (0.067) 0.996 4 5.240 (0.234) 5.155 (0.252) 0.984 8 4.370 (0.241) 4.111 (0.342) 0.941 16 4.152 (0.112) 4.113 (0.164) 0.991 32 2.579 (0.099) 4.099 (0.127) 1.589 36 2.604 (0.066) 4.005 (0.104) 1.538 72 2.028 (0.091) 4.024 (0.112) 1.984 108 2.079 (0.106) 3.997 (0.093) 1.923 142 1.858 (0.103) 3.955 (0.109) 2.129 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 0.530 (0.013) 0.533 (0.011) 1.006 2 0.839 (0.043) 0.847 (0.031) 1.010 4 0.758 (0.021) 0.764 (0.018) 1.008 8 0.677 (0.022) 0.682 (0.016) 1.008 16 0.714 (0.023) 0.814 (0.027) 1.140 32 0.765 (0.040) 1.168 (0.032) 1.527 36 0.706 (0.023) 1.139 (0.066) 1.614 72 0.624 (0.017) 1.184 (0.026) 1.898 108 0.605 (0.013) 1.147 (0.023) 1.894 142 0.593 (0.012) 1.131 (0.019) 1.908 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 | 18 + arch/arm/include/asm/mcs_spinlock.h | 6 +- arch/x86/Kconfig | 20 + arch/x86/include/asm/qspinlock.h | 6 + arch/x86/kernel/alternative.c | 2 + include/asm-generic/mcs_spinlock.h | 4 +- kernel/locking/mcs_spinlock.h | 20 +- kernel/locking/qspinlock.c | 82 +++- kernel/locking/qspinlock_cna.h | 407 ++++++++++++++++++ kernel/locking/qspinlock_paravirt.h | 2 +- 10 files changed, 544 insertions(+), 23 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.21.1 (Apple Git-122.3)
