On Tue, Dec 11, 2018 at 03:33:47PM -0800, Song Liu wrote:
> For better performance analysis of BPF programs, this patch introduces
> PERF_RECORD_BPF_EVENT, a new perf_event_type that exposes BPF program
> load/unload information to user space.
>
> Each BPF program may contain up to BPF_MAX_SUBPROGS (256) sub programs.
> The following example shows kernel symbols for a BPF program with 7
> sub programs:
>
> ffffffffa0257cf9 t bpf_prog_b07ccb89267cf242_F
> ffffffffa02592e1 t bpf_prog_2dcecc18072623fc_F
> ffffffffa025b0e9 t bpf_prog_bb7a405ebaec5d5c_F
> ffffffffa025dd2c t bpf_prog_a7540d4a39ec1fc7_F
> ffffffffa025fcca t bpf_prog_05762d4ade0e3737_F
> ffffffffa026108f t bpf_prog_db4bd11e35df90d4_F
> ffffffffa0263f00 t bpf_prog_89d64e4abf0f0126_F
> ffffffffa0257cf9 t bpf_prog_ae31629322c4b018__dummy_tracepoi
Doesn't BPF have enough information to generate 'saner' names? Going by
the thing below, these sub-progs are actually functions, right?
> /*
> * Record different types of bpf events:
> * enum perf_bpf_event_type {
> * PERF_BPF_EVENT_UNKNOWN = 0,
> * PERF_BPF_EVENT_PROG_LOAD = 1,
> * PERF_BPF_EVENT_PROG_UNLOAD = 2,
> * };
> *
> * struct {
> * struct perf_event_header header;
> * u32 type;
> * u32 flags;
> * u32 id; // prog_id or other id
> * u32 sub_id; // subprog id
> *
> * // for bpf_prog types, bpf prog or subprog
> * u8 tag[BPF_TAG_SIZE];
> * u64 addr;
> * u64 len;
> * char name[];
> * struct sample_id sample_id;
> * };
> */
Isn't this mixing two different things (poorly)? The kallsym update and
the BPF load/unload ?
And while this tracks the bpf kallsyms, it does not do all kallsyms.
.... Oooh, I see the problem, everybody is doing their own custom
kallsym_{add,del}() thing, instead of having that in generic code :-(
This, for example, doesn't track module load/unload nor ftrace
trampolines, even though both affect kallsyms.
> +void perf_event_bpf_event_prog(enum perf_bpf_event_type type,
> + struct bpf_prog *prog)
> +{
> + if (!atomic_read(&nr_bpf_events))
> + return;
> +
> + if (type != PERF_BPF_EVENT_PROG_LOAD &&
> + type != PERF_BPF_EVENT_PROG_UNLOAD)
> + return;
> +
> + if (prog->aux->func_cnt == 0) {
> + perf_event_bpf_event_subprog(type, prog,
> + prog->aux->id, 0);
> + } else {
> + int i;
> +
> + for (i = 0; i < prog->aux->func_cnt; i++)
> + perf_event_bpf_event_subprog(type, prog->aux->func[i],
> + prog->aux->id, i);
> + }
> +}
