Re: [PATCH v3 2/4] perf lock contention: Run BPF slab cache iterator

[Alexei Starovoitov]

On Thu, Dec 19, 2024 at 10:01 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> +struct bpf_iter__kmem_cache___new {
> +       struct kmem_cache *s;
> +} __attribute__((preserve_access_index));
> +
> +SEC("iter/kmem_cache")
> +int slab_cache_iter(void *ctx)
> +{
> +       struct kmem_cache *s = NULL;
> +       struct slab_cache_data d;
> +       const char *nameptr;
> +
> +       if (bpf_core_type_exists(struct bpf_iter__kmem_cache)) {
> +               struct bpf_iter__kmem_cache___new *iter = ctx;
> +
> +               s = BPF_CORE_READ(iter, s);
> +       }
> +
> +       if (s == NULL)
> +               return 0;
> +
> +       nameptr = BPF_CORE_READ(s, name);

since the feature depends on the latest kernel please use
direct access. There is no need to use BPF_CORE_READ() to
be compatible with old kernels.
Just iter->s and s->name will work and will be much faster.
Underneath these loads will be marked with PROBE_MEM flag and
will be equivalent to probe_read_kernel calls, but faster
since the whole thing will be inlined by JITs.