Hi Will, On Mon, Dec 30, 2019 at 02:40:37PM -0500, Alex Kogan wrote: > Minor changes from v7 based on feedback from Longman: > ----------------------------------------------------- > > - Move __init functions from alternative.c to qspinlock_cna.h > > - Introduce enum for return values from cna_pre_scan(), for better > readability. > > - Add/revise a few comments to improve readability. > > > 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 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. After acquiring the MCS lock and > before acquiring the spinlock, the lock holder scans the main queue > looking for a thread running on the same node (pre-scan). 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. If such T > is not found, we make another scan of the main 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 > 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 > number of intra-node lock hand-offs. > > More details are available at https://urldefense.proofpoint.com/v2/url?u=https-3A__arxiv.org_abs_1810.05600&d=DwIDAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=G9w4KsPaQLACBfGCL35PtiRH996yqJDxAZwrWegU2qQ&m=AoOLTQlgNjtdBvY_yWd6ViBXrVM6o2wqXOdFA4B_F2A&s=yUjG9gfi3BtLKDEjgki86h52GVXMvDQ6ZClMvoIG034&e= . > > The series applies on top of v5.5.0-rc2, commit ea200dec51. > Performance numbers are available in previous revisions > of the series. > > 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: 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 | 400 ++++++++++++++++++ > kernel/locking/qspinlock_paravirt.h | 2 +- > 10 files changed, 537 insertions(+), 23 deletions(-) > create mode 100644 kernel/locking/qspinlock_cna.h > > -- > 2.21.0 (Apple Git-122.2) > Tried out queued spinlock slowpath improvements on arm64 (ThunderX2) by hardwiring CNA APIs to queued_spin_lock_slowpath() and numbers are pretty good with the CNA changes. Speed-up on v5.5-rc4 kernel: will-it-scale/open1_threads: #thr speed-up 1 1.00 2 0.97 4 0.98 8 1.02 16 0.95 32 1.63 64 1.70 128 2.09 224 2.16 will-it-scale/lock2_threads: #thr speed-up 1 0.98 2 0.99 4 0.90 8 0.98 16 0.99 32 1.52 64 2.31 128 2.25 224 2.04 #thr - number of threads speed-up - number with CNA patch / number with stock kernel Please share your thoughts on best way to enable this series on arm64. Thanks, Shijith
