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Date:   Wed, 20 May 2020 18:13:31 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Changbin Du <changbin.du@gmail.com>
Cc:     Jiri Olsa <jolsa@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 17/19] perf ftrace: add option -d/--delay to delay tracing
Message-ID: <20200520211331.GA3898@kernel.org>
References: <20200510150628.16610-1-changbin.du@gmail.com>
 <20200510150628.16610-18-changbin.du@gmail.com>
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Em Sun, May 10, 2020 at 11:06:26PM +0800, Changbin Du escreveu:
> This adds an option '-d/--delay' to allow us to start tracing some
> times later after workload is launched.

[acme@five perf]$ perf record -h delay

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -D, --delay <n>       ms to wait before starting measurement after program start

[acme@five perf]$
 
> Signed-off-by: Changbin Du <changbin.du@gmail.com>
> ---
>  tools/perf/builtin-ftrace.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 8d04e5afe2d3..d376b37c53fc 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -49,6 +49,7 @@ struct perf_ftrace {
>  	bool			trace_children;
>  	unsigned		buffer_size_kb;
>  	bool			no_pager;
> +	unsigned		initial_delay;
>  };
>  
>  struct filter_entry {
> @@ -617,13 +618,23 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
>  	/* display column headers */
>  	read_tracing_file_to_stdout("trace");
>  
> -	if (write_tracing_file("tracing_on", "1") < 0) {
> -		pr_err("can't enable tracing\n");
> -		goto out_close_fd;
> +	if (!ftrace->initial_delay) {
> +		if (write_tracing_file("tracing_on", "1") < 0) {
> +			pr_err("can't enable tracing\n");
> +			goto out_close_fd;
> +		}
>  	}
>  
>  	perf_evlist__start_workload(ftrace->evlist);
>  
> +	if (ftrace->initial_delay) {
> +		usleep(ftrace->initial_delay * 1000);
> +		if (write_tracing_file("tracing_on", "1") < 0) {
> +			pr_err("can't enable tracing\n");
> +			goto out_close_fd;
> +		}
> +	}
> +
>  	while (!done) {
>  		if (poll(&pollfd, 1, -1) < 0)
>  			break;
> @@ -747,6 +758,8 @@ int cmd_ftrace(int argc, const char **argv)
>  		     "size of per cpu buffer in kb"),
>  	OPT_BOOLEAN('P', "no-pager", &ftrace.no_pager,
>  		    "Do not use pager"),
> +	OPT_UINTEGER('d', "delay", &ftrace.initial_delay,
> +		     "Wait <n> ms before tracing"),
>  	OPT_END()
>  	};
>  
> -- 
> 2.25.1
> 

-- 

- Arnaldo