On 1/21/20 8:29 AM, 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. I actually had similar question before, but having the capability of changing the default with boot time parameter alleviate some of my concern. I will certainly like to see actual data on how different values will affect the performance of the code. Cheers, Longman
