Changes from v3: ---------------- - Store encoded pointer in @locked, as suggested by Longman. As a result, mcs_node size is now intact. - Add a new kernel boot command-line option "numa_spinlock=on/off/auto", which may override the selection of the NUMA-aware spinlock during boot, as requested by Longman. - Add a dependency on QUEUED_SPINLOCKS to NUMA_AWARE_SPINLOCKS and fix the help text, as requested by Longman. - Init the cna_node state in early_initcall(), so we do it only once instead of every time the node is used, as suggested by Longman. - Rename macros & functions, refactor cna_try_find_next() (former find_successor()), as suggested by Peter. - Add more commentary, including textual graphics to CNA, as suggested by Longman and Peter. - Change the argument in probably() to num_bits, as suggested by Peter. 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 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 is about 3% from the average. The 'stock' kernel is v5.3.0-rc2, commit 74e6314df6bc, 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 2.692 (0.094) 2.660 (0.100) 0.988 2 2.634 (0.122) 2.631 (0.136) 0.999 4 4.152 (0.090) 4.370 (0.152) 1.052 8 5.420 (0.112) 6.978 (0.237) 1.288 16 6.593 (0.141) 8.597 (0.253) 1.304 32 7.335 (0.168) 9.296 (0.223) 1.267 36 7.505 (0.195) 9.329 (0.251) 1.243 72 6.552 (0.180) 9.846 (0.256) 1.503 108 6.194 (0.114) 9.901 (0.196) 1.599 142 5.706 (0.093) 9.866 (0.193) 1.729 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 0.537 (0.001) 0.539 (0.001) 1.003 2 0.808 (0.021) 0.799 (0.022) 0.988 4 1.434 (0.031) 1.425 (0.024) 0.994 8 1.727 (0.102) 1.725 (0.115) 0.999 16 1.714 (0.094) 1.739 (0.082) 1.015 32 0.929 (0.070) 1.677 (0.081) 1.804 36 0.935 (0.087) 1.694 (0.079) 1.812 72 0.842 (0.040) 1.687 (0.069) 2.004 108 0.842 (0.049) 1.737 (0.074) 2.063 142 0.823 (0.049) 1.744 (0.085) 2.119 and will-it-scale/lock2_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 1.601 (0.013) 1.615 (0.006) 1.009 2 2.719 (0.060) 2.741 (0.060) 1.008 4 5.269 (0.392) 5.336 (0.272) 1.013 8 4.061 (0.302) 4.210 (0.311) 1.037 16 4.081 (0.113) 4.170 (0.133) 1.022 32 2.503 (0.104) 4.029 (0.120) 1.610 36 2.493 (0.104) 3.987 (0.111) 1.599 72 1.966 (0.092) 3.968 (0.118) 2.019 108 2.084 (0.116) 3.951 (0.121) 1.896 142 1.925 (0.123) 3.877 (0.088) 2.014 We also evaluated the patch on a single-node machine (Intel i7-4770 with 4 hyperthreaded cores) with will-it-scale, and observed no meaningful performance impact, as expected. For instance, below are results for will-it-scale/open1_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 0.866 (0.003) 0.867 (0.001) 1.001 2 1.463 (0.014) 1.463 (0.019) 1.000 4 2.656 (0.052) 2.671 (0.052) 1.005 6 2.872 (0.054) 2.857 (0.045) 0.995 Furthermore, we evaluated the patch in the paravirt setup, booting the kernel with virtme (qemu) and $(nproc) cores on the same Oracle X5-4 server as above. We run will-it-scale benchmarks, and once again observed no meaningful performance impact. For instance, below are results for will-it-scale/open1_threads: #thr stock patch-CNA speedup (patch-CNA/stock) 1 0.743 (0.009) 0.747 (0.011) 1.005 2 0.615 (0.031) 0.611 (0.040) 0.993 4 0.629 (0.027) 0.619 (0.034) 0.984 8 0.580 (0.023) 0.574 (0.022) 0.991 16 0.676 (0.019) 0.680 (0.019) 1.006 32 0.566 (0.046) 0.562 (0.026) 0.992 36 0.545 (0.047) 0.544 (0.025) 1.000 72 0.358 (0.010) 0.361 (0.011) 1.009 108 0.353 (0.013) 0.356 (0.012) 1.010 142 0.350 (0.010) 0.355 (0.008) 1.013 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 0.535 (0.010) 0.530 (0.020) 0.990 2 0.659 (0.023) 0.675 (0.030) 1.024 4 0.709 (0.017) 0.707 (0.028) 0.998 8 0.671 (0.026) 0.670 (0.024) 0.999 16 0.716 (0.017) 0.717 (0.020) 1.002 32 0.741 (0.036) 1.040 (0.090) 1.403 36 0.727 (0.042) 1.152 (0.086) 1.585 72 0.639 (0.028) 1.192 (0.023) 1.863 108 0.621 (0.024) 1.181 (0.028) 1.902 142 0.604 (0.015) 1.158 (0.028) 1.919 Further comments are welcome and appreciated. Alex Kogan (5): locking/qspinlock: Rename arch_mcs_spin_unlock_contended to arch_mcs_pass_lock and make it 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 | 19 +++ arch/x86/include/asm/qspinlock.h | 4 + arch/x86/kernel/alternative.c | 41 ++++++ kernel/locking/mcs_spinlock.h | 8 +- kernel/locking/qspinlock.c | 69 ++++++++- kernel/locking/qspinlock_cna.h | 276 ++++++++++++++++++++++++++++++++++++ 7 files changed, 409 insertions(+), 12 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.11.0 (Apple Git-81)
