Hello, On Sat, Feb 08, 2025 at 10:19:38AM +0100, Andrea Righi wrote: ... > > This is contingent on scx_builtin_idle_per_node, right? It's confusing for > > CPU -> node mapping function to return NUMA_NO_NODE depending on an ops > > flag. Shouldn't this be a generic mapping function? > > The idea is that BPF schedulers can use this kfunc to determine the right > idle cpumask to use, for example a typical usage could be: > > int node = scx_bpf_cpu_node(prev_cpu); > s32 cpu = scx_bpf_pick_idle_cpu_in_node(p->cpus_ptr, node, SCX_PICK_IDLE_IN_NODE); > > Or: > > int node = scx_bpf_cpu_node(prev_cpu); > const struct cpumask *idle_cpumask = scx_bpf_get_idle_cpumask_node(node); > > When SCX_OPS_BUILTIN_IDLE_PER_NODE is disabled, we need to point to the > global idle cpumask, that is identified by NUMA_NO_NODE, so this is why we > can return NUMA_NO_NODE fro scx_bpf_cpu_node(). > > Do you think we should make this more clear / document this better. Or do > you think we should use a different API? I think this is too error-prone. It'd be really easy for users to assume that scx_bpf_cpu_node() always returns the NUMA node for the given CPU which can lead to really subtle surprises. Why even allow e.g. scx_bpf_get_idle_cpumask_node() if IDLE_PER_NODE is not enabled? Thanks. -- tejun
