On Wed, Jan 30, 2019 at 10:01:32PM -0500, Alex Kogan wrote: > Lock throughput can be increased by handing a lock to a waiter on the > same NUMA socket as the lock holder, provided care is taken to avoid > starvation of waiters on other NUMA sockets. This patch introduces CNA > (compact NUMA-aware lock) as the slow path for qspinlock. Since you use NUMA, use the term node, not socket. The two are not strictly related. > 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 > socket as the current lock holder, and a secondary queue for threads > running on other sockets. Threads record the ID of the socket 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 > socket. 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. > > Full details are available at https://arxiv.org/abs/1810.05600. Full details really should also be in the Changelog. You can skip much of the academic bla-bla, but the Changelog should be self contained. > 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 5 runs) of the > total number of ops (x10^7) reported at the end of each run. The stock > kernel is v4.20.0-rc4+ compiled in the default configuration. > > #thr stock patched speedup (patched/stock) > 1 2.710 2.715 1.002 > 2 3.108 3.001 0.966 > 4 4.194 3.919 0.934 So low contention is actually worse. Funnily low contention is the majority of our locks and is _really_ important. > 8 5.309 6.894 1.299 > 16 6.722 9.094 1.353 > 32 7.314 9.885 1.352 > 36 7.562 9.855 1.303 > 72 6.696 10.358 1.547 > 108 6.364 10.181 1.600 > 142 6.179 10.178 1.647 > > When the kernel is compiled with lockstat enabled, CNA I'll ignore that, lockstat/lockdep enabled runs are not what one would call performance relevant.
