Re: [PATCH 6/6] sched_ext: idle: Introduce node-aware idle cpu kfunc helpers

Tejun Heo
2025-02-07T22:39:58Z

Hello,

On Fri, Feb 07, 2025 at 09:40:53PM +0100, Andrea Righi wrote:
> +/**
> + * scx_bpf_cpu_to_node - Return the NUMA node the given @cpu belongs to
> + */
> +__bpf_kfunc int scx_bpf_cpu_to_node(s32 cpu)

Maybe scx_bpf_cpu_node() to be in line with scx_bpf_task_cpu/cgroup()?

> +{
> +#ifdef CONFIG_NUMA
> + if (cpu < 0 || cpu >= nr_cpu_ids)
> + return -EINVAL;

Use ops_cpu_valid()? Otherwise, we can end up calling cpu_to_node() with an
impossible CPU. Also, I don't think CPU -> node mapping function should be
able to return an error value. It should just trigger ops error.

> +
> + return idle_cpu_to_node(cpu);

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?

> index 50e1499ae0935..caa1a80f9a60c 100644
> --- a/tools/sched_ext/include/scx/compat.bpf.h
> +++ b/tools/sched_ext/include/scx/compat.bpf.h
> @@ -130,6 +130,25 @@ bool scx_bpf_dispatch_vtime_from_dsq___compat(struct bpf_iter_scx_dsq *it__iter,
> scx_bpf_now() : \
> bpf_ktime_get_ns())
>
> +#define __COMPAT_scx_bpf_cpu_to_node(cpu) \
> + (bpf_ksym_exists(scx_bpf_cpu_to_node) ? \
> + scx_bpf_cpu_to_node(cpu) : 0)
> +
> +#define __COMPAT_scx_bpf_get_idle_cpumask_node(node) \
> + (bpf_ksym_exists(scx_bpf_get_idle_cpumask_node) ? \
> + scx_bpf_get_idle_cpumask_node(node) : \
> + scx_bpf_get_idle_cpumask()) \
> +
> +#define __COMPAT_scx_bpf_get_idle_smtmask_node(node) \
> + (bpf_ksym_exists(scx_bpf_get_idle_smtmask_node) ? \
> + scx_bpf_get_idle_smtmask_node(node) : \
> + scx_bpf_get_idle_smtmask())
> +
> +#define __COMPAT_scx_bpf_pick_idle_cpu_node(cpus_allowed, node, flags) \
> + (bpf_ksym_exists(scx_bpf_pick_idle_cpu_node) ? \
> + scx_bpf_pick_idle_cpu_node(cpus_allowed, node, flags) : \
> + scx_bpf_pick_idle_cpu(cpus_allowed, flags))

Can you please document when these compat macros can be dropped? Also,
shouldn't it also provide a compat macro for the new ops flag using
__COMPAT_ENUM_OR_ZERO()? Otherwise, trying to load new binary using the new
flag on an older kernel will fail, right?

Thanks.

--
tejun