Re: [PATCH 13/13] perf tools: Use same BPF program if arguments are identical

From: Wangnan (F)
Date: Mon Nov 16 2015 - 22:06:34 EST




On 2015/11/16 20:10, Wang Nan wrote:
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@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
---

[SNIP]

@@ -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);
+

We can change 0xff to -1 like previous patches. Will do it by resending.

Thank you.

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