On Tue, Jan 21, 2020 at 02:29:49PM +0100, Peter Zijlstra wrote: > On Mon, Dec 30, 2019 at 02:40:41PM -0500, Alex Kogan wrote: > > > +/* > > + * Controls the threshold for the number of intra-node lock hand-offs before > > + * the NUMA-aware variant of spinlock is forced to be passed to a thread on > > + * another NUMA node. By default, the chosen value provides reasonable > > + * long-term fairness without sacrificing performance compared to a lock > > + * that does not have any fairness guarantees. The default setting can > > + * be changed with the "numa_spinlock_threshold" boot option. > > + */ > > +int intra_node_handoff_threshold __ro_after_init = 1 << 16; > > There is a distinct lack of quantitative data to back up that > 'reasonable' claim there. > > Where is the table of inter-node latencies observed for the various > values tested, and on what criteria is this number deemed reasonable? > > To me, 64k lock hold times seems like a giant number, entirely outside > of reasonable. Daniel, IIRC you just did a paper on constructing worst case latencies from measuring pieces. Do you have data on average lock hold times?
