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Message-ID: <CAM9d7ch8RUgf8V1hi=ccgV84XSfujuWtUKKgre8eQdGmtdiFLA@mail.gmail.com> Date: Fri, 30 Sep 2022 19:31:17 -0700 From: Namhyung Kim <namhyung@...nel.org> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>, cgroups <cgroups@...r.kernel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...nel.org>, LKML <linux-kernel@...r.kernel.org>, linux-perf-users <linux-perf-users@...r.kernel.org>, Song Liu <songliubraving@...com>, bpf <bpf@...r.kernel.org> Subject: Re: [PATCH] perf stat: Support old kernels for bperf cgroup counting Hello, On Fri, Sep 30, 2022 at 3:48 PM Andrii Nakryiko <andrii.nakryiko@...il.com> wrote: > > On Wed, Sep 21, 2022 at 9:21 PM Namhyung Kim <namhyung@...nel.org> wrote: > > > > The recent change in the cgroup will break the backward compatiblity in > > the BPF program. It should support both old and new kernels using BPF > > CO-RE technique. > > > > Like the task_struct->__state handling in the offcpu analysis, we can > > check the field name in the cgroup struct. > > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org> > > --- > > Arnaldo, I think this should go through the cgroup tree since it depends > > on the earlier change there. I don't think it'd conflict with other > > perf changes but please let me know if you see any trouble, thanks! > > > > tools/perf/util/bpf_skel/bperf_cgroup.bpf.c | 29 ++++++++++++++++++++- > > 1 file changed, 28 insertions(+), 1 deletion(-) > > > > diff --git a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > index 488bd398f01d..4fe61043de04 100644 > > --- a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > +++ b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > @@ -43,12 +43,39 @@ struct { > > __uint(value_size, sizeof(struct bpf_perf_event_value)); > > } cgrp_readings SEC(".maps"); > > > > +/* new kernel cgroup definition */ > > +struct cgroup___new { > > + int level; > > + struct cgroup *ancestors[]; > > +} __attribute__((preserve_access_index)); > > + > > +/* old kernel cgroup definition */ > > +struct cgroup___old { > > + int level; > > + u64 ancestor_ids[]; > > +} __attribute__((preserve_access_index)); > > + > > const volatile __u32 num_events = 1; > > const volatile __u32 num_cpus = 1; > > > > int enabled = 0; > > int use_cgroup_v2 = 0; > > > > +static inline __u64 get_cgroup_v1_ancestor_id(struct cgroup *cgrp, int level) > > +{ > > + /* recast pointer to capture new type for compiler */ > > + struct cgroup___new *cgrp_new = (void *)cgrp; > > + > > + if (bpf_core_field_exists(cgrp_new->ancestors)) { > > + return BPF_CORE_READ(cgrp_new, ancestors[level], kn, id); > > have you checked generated BPF code for this ancestors[level] access? > I'd expect CO-RE relocation for finding ancestors offset and then just > normal + level * 8 arithmetic, but would be nice to confirm. Apart > from this, looks good to me: > > Acked-by: Andrii Nakryiko <andrii@...nel.org> Thanks for your review! How can I check the generated code? Do you have something works with skeletons or do I have to save the BPF object somehow during the build? Thanks, Namhyung
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