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Subject[PATCH 13/13] perf tools: Use same BPF program if arguments are identical
Date
This patch allows creating only one BPF program for different
'probe_trace_event'(tev) generated by one 'perf_probe_event'(pev), if
their prologues are identical.

This is done by comparing argument list of different tev, and maps type
of prologue and tev using a mapping array. This patch utilizes qsort to
sort tevs. After sorting, tevs with identical argument list will be
grouped together.

Test result:

Sample BPF program:

SEC("inlines=no\n"
"func=SyS_dup? oldfd")
int func(void *ctx)
{
return 1;
}

It would probe at SyS_dup2 and SyS_dup3, extracts oldfd as its argument.

Following cmdline shows BPF program loaded into kernel by perf:

# ./perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog

Before this patch:

# ./perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog
[1] 24858
lrwx------ 1 root root 64 Nov 14 04:09 3 -> anon_inode:bpf-prog
lrwx------ 1 root root 64 Nov 14 04:09 4 -> anon_inode:bpf-prog
...

After this patch:

# ./perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog
[1] 25699
lrwx------ 1 root root 64 Nov 14 04:10 3 -> anon_inode:bpf-prog
...

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
tools/perf/util/bpf-loader.c | 136 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 129 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index cad0d0f..86c50b9 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -38,6 +38,8 @@ struct bpf_prog_priv {
struct perf_probe_event pev;
bool need_prologue;
struct bpf_insn *insns_buf;
+ int nr_types;
+ int *type_mapping;
};

static bool libbpf_initialized;
@@ -113,6 +115,7 @@ bpf_prog_priv__clear(struct bpf_program *prog __maybe_unused,

cleanup_perf_probe_events(&priv->pev, 1);
zfree(&priv->insns_buf);
+ zfree(&priv->type_mapping);
free(priv);
}

@@ -381,7 +384,7 @@ preproc_gen_prologue(struct bpf_program *prog, int n,
struct bpf_prog_priv *priv;
struct bpf_insn *buf;
size_t prologue_cnt = 0;
- int err;
+ int i, err;

err = bpf_program__get_private(prog, (void **)&priv);
if (err || !priv)
@@ -389,10 +392,20 @@ preproc_gen_prologue(struct bpf_program *prog, int n,

pev = &priv->pev;

- if (n < 0 || n >= pev->ntevs)
+ if (n < 0 || n >= priv->nr_types)
goto errout;

- tev = &pev->tevs[n];
+ /* Find a tev belongs to that type */
+ for (i = 0; i < pev->ntevs; i++)
+ if (priv->type_mapping[i] == n)
+ break;
+
+ if (i >= pev->ntevs) {
+ pr_debug("Internal error: prologue type %d not found\n", n);
+ return -BPF_LOADER_ERRNO__PROLOGUE;
+ }
+
+ tev = &pev->tevs[i];

buf = priv->insns_buf;
err = bpf__gen_prologue(tev->args, tev->nargs,
@@ -423,6 +436,101 @@ errout:
return -BPF_LOADER_ERRNO__PROLOGUE;
}

+/*
+ * compare_tev_args is reflexive, transitive and antisymmetric.
+ * I can proof it but this margin is too narrow to contain.
+ */
+static int compare_tev_args(const void *ptev1, const void *ptev2)
+{
+ int i, ret;
+ const struct probe_trace_event *tev1 =
+ *(const struct probe_trace_event **)ptev1;
+ const struct probe_trace_event *tev2 =
+ *(const struct probe_trace_event **)ptev2;
+
+ ret = tev2->nargs - tev1->nargs;
+ if (ret)
+ return ret;
+
+ for (i = 0; i < tev1->nargs; i++) {
+ struct probe_trace_arg *arg1, *arg2;
+ struct probe_trace_arg_ref *ref1, *ref2;
+
+ arg1 = &tev1->args[i];
+ arg2 = &tev2->args[i];
+
+ ret = strcmp(arg1->value, arg2->value);
+ if (ret)
+ return ret;
+
+ ref1 = arg1->ref;
+ ref2 = arg2->ref;
+
+ while (ref1 && ref2) {
+ ret = ref2->offset - ref1->offset;
+ if (ret)
+ return ret;
+
+ ref1 = ref1->next;
+ ref2 = ref2->next;
+ }
+
+ if (ref1 || ref2)
+ return ref2 ? 1 : -1;
+ }
+
+ return 0;
+}
+
+/*
+ * Assign a type number to each tevs in a pev.
+ * mapping is an array with same slots as tevs in that pev.
+ * nr_types will be set to number of types.
+ */
+static int map_prologue(struct perf_probe_event *pev, int *mapping,
+ int *nr_types)
+{
+ int i, type = 0;
+ struct probe_trace_event **ptevs;
+
+ size_t array_sz = sizeof(*ptevs) * pev->ntevs;
+
+ ptevs = malloc(array_sz);
+ if (!ptevs) {
+ pr_debug("No ehough memory: alloc ptevs failed\n");
+ return -ENOMEM;
+ }
+
+ pr_debug("In map_prologue, ntevs=%d\n", pev->ntevs);
+ for (i = 0; i < pev->ntevs; i++)
+ ptevs[i] = &pev->tevs[i];
+
+ qsort(ptevs, pev->ntevs, sizeof(*ptevs),
+ compare_tev_args);
+
+ for (i = 0; i < pev->ntevs; i++) {
+ int n;
+
+ n = ptevs[i] - pev->tevs;
+ if (i == 0) {
+ mapping[n] = type;
+ pr_debug("mapping[%d]=%d\n", n, type);
+ continue;
+ }
+
+ if (compare_tev_args(ptevs + i, ptevs + i - 1) == 0)
+ mapping[n] = type;
+ else
+ mapping[n] = ++type;
+
+ pr_debug("mapping[%d]=%d\n", n, mapping[n]);
+ }
+ free(ptevs);
+ *nr_types = type + 1;
+
+ return 0;
+}
+
static int hook_load_preprocessor(struct bpf_program *prog)
{
struct perf_probe_event *pev;
@@ -462,7 +570,19 @@ static int hook_load_preprocessor(struct bpf_program *prog)
return -ENOMEM;
}

- err = bpf_program__set_prep(prog, pev->ntevs,
+ priv->type_mapping = malloc(sizeof(int) * pev->ntevs);
+ if (!priv->type_mapping) {
+ pr_debug("No enough memory: alloc type_mapping failed\n");
+ return -ENOMEM;
+ }
+ memset(priv->type_mapping, 0xff,
+ sizeof(int) * pev->ntevs);
+
+ err = map_prologue(pev, priv->type_mapping, &priv->nr_types);
+ if (err)
+ return err;
+
+ err = bpf_program__set_prep(prog, priv->nr_types,
preproc_gen_prologue);
return err;
}
@@ -596,9 +716,11 @@ int bpf__foreach_tev(struct bpf_object *obj,
for (i = 0; i < pev->ntevs; i++) {
tev = &pev->tevs[i];

- if (priv->need_prologue)
- fd = bpf_program__nth_fd(prog, i);
- else
+ if (priv->need_prologue) {
+ int type = priv->type_mapping[i];
+
+ fd = bpf_program__nth_fd(prog, type);
+ } else
fd = bpf_program__fd(prog);

if (fd < 0) {
--
1.8.3.4


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