Re: [PATCH v3 perf, bpf-next 1/4] perf, bpf: Introduce PERF_RECORD_BPF_EVENT

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);
+	}
+}