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libbpf-tools/offcputime: Use CO-RE operation to read kernel data #4471

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libbpf-tools/offcputime: Use CO-RE operation to read kernel data #4471

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8 changes: 4 additions & 4 deletions libbpf-tools/offcputime.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,15 +66,15 @@ int BPF_PROG(sched_switch, bool preempt, struct task_struct *prev, struct task_s
u32 pid;

if (allow_record(prev)) {
pid = prev->pid;
pid = BPF_CORE_READ(prev, pid);
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tp_btf is BTF-awared, pointer chasing should work, right ?

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@ekyooo ekyooo Feb 9, 2023 •
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Oh... I didn't know that. Thank you for the information. Does tp_btf support depend on kernel version?
A segfault occurred when running the default version of offfcputime on my Linux v5.4 kernel environment. So I switched tp_btf to tracepoint as below. So this patch was needed.

-SEC("tp_btf/sched_switch")
+SEC("tracepoint/sched/sched_switch")

Could you please tell me if tp_btf is supported in Linux v5.4 as well?
Thank you in advance.

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Ok. I got information from another engineer that tp_btf is not supported in Linux v5.4. I abandon this patch. Thank you.

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See #4231.

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Oh..!! Thank you. I'll read it carefully.

/* To distinguish idle threads of different cores */
if (!pid)
pid = bpf_get_smp_processor_id();
i_key.key.pid = pid;
i_key.key.tgid = prev->tgid;
i_key.key.tgid = BPF_CORE_READ(prev, tgid);
i_key.start_ts = bpf_ktime_get_ns();

if (prev->flags & PF_KTHREAD)
if (BPF_CORE_READ(prev, flags) & PF_KTHREAD)
i_key.key.user_stack_id = -1;
else
i_key.key.user_stack_id =
Expand All @@ -87,7 +87,7 @@ int BPF_PROG(sched_switch, bool preempt, struct task_struct *prev, struct task_s
bpf_map_update_elem(&info, &i_key.key, &val, BPF_NOEXIST);
}

pid = next->pid;
pid = BPF_CORE_READ(next, pid);
i_keyp = bpf_map_lookup_elem(&start, &pid);
if (!i_keyp)
return 0;
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