On Fri, 2019-10-11 at 10:09 -0400, Waiman Long wrote: > At each invocation of rt_spin_unlock(), cpumask_weight() is called > via migrate_enable_update_cpus_allowed() to recompute the weight of > cpus_mask which doesn't change that often. > > The following is a sample output of perf-record running the testpmd > microbenchmark on an RT kernel: > > 34.77% 1.65% testpmd [kernel.kallsyms] [k] rt_spin_unlock > 34.32% 2.52% testpmd [kernel.kallsyms] [k] migrate_enable > 21.76% 21.76% testpmd [kernel.kallsyms] [k] __bitmap_weight > > By adding an extra variable to keep track of the weight of cpus_mask, > we could eliminate the frequent call to cpumask_weight() and replace > it with simple assignment. Can you try this with my migrate disable patchset (which makes amigrate_enable_update_cpus_allowed() be called much less often) and see if caching nr_cpus_allowed still makes a difference? -Scott
