On Sat, Dec 21, 2024 at 03:55:32PM -0800, Namhyung Kim wrote:
> Hi Alexei,
>
> On Fri, Dec 20, 2024 at 03:52:36PM -0800, Alexei Starovoitov wrote:
> > 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.
>
> Oh, thanks for your review. I thought it was requried, but it'd
> be definitely better if we can access them directly. I'll fold
> the below to v4, unless Arnaldo does it first. :)
I'll check and adjust, thanks everybody :-)
- Arnaldo
> Thanks,
> Namhyung
>
>
> ---8<---
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index 6c771ef751d83b43..6533ea9b044c71d1 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -635,13 +635,13 @@ int slab_cache_iter(void *ctx)
> if (bpf_core_type_exists(struct bpf_iter__kmem_cache)) {
> struct bpf_iter__kmem_cache___new *iter = ctx;
>
> - s = BPF_CORE_READ(iter, s);
> + s = iter->s;
> }
>
> if (s == NULL)
> return 0;
>
> - nameptr = BPF_CORE_READ(s, name);
> + nameptr = s->name;
> bpf_probe_read_kernel_str(d.name, sizeof(d.name), nameptr);
>
> d.id = ++slab_cache_id << LCB_F_SLAB_ID_SHIFT;
