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

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Message-ID: <564A9985.20404@huawei.com>
Date:	Tue, 17 Nov 2015 11:05:41 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	<acme@...nel.org>, <masami.hiramatsu.pt@...achi.com>,
	<ast@...nel.org>
CC:	<lizefan@...wei.com>, <pi3orama@....com>,
	<linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 13/13] perf tools: Use same BPF program if arguments are
 identical



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@...wei.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---

[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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