linux-kernel - Re: [PATCH V3 1/5] perf,tools: introduce generic FEAT for CPU attributes

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Date:	Wed, 29 Jul 2015 14:31:17 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	kan.liang@...el.com
Cc:	a.p.zijlstra@...llo.nl, acme@...nel.org, luto@...nel.org,
	mingo@...hat.com, eranian@...gle.com, ak@...ux.intel.com,
	mark.rutland@....com, adrian.hunter@...el.com, jolsa@...nel.org,
	namhyung@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/5] perf,tools: introduce generic FEAT for CPU
 attributes

On Tue, Jul 28, 2015 at 07:29:31AM -0400, kan.liang@...el.com wrote:

SNIP

>  
> +static void print_cpu_attributes(struct perf_header *ph, int fd __maybe_unused, FILE *fp)
> +{
> +	fprintf(fp, "# CPU attributes: max frequency = %lu KHz\n", ph->env.cpu_attr[PERF_HEADER_CPU_MAX_FREQ]);
> +}
> +
>  static void print_branch_stack(struct perf_header *ph __maybe_unused,
>  			       int fd __maybe_unused, FILE *fp)
>  {
> @@ -1471,6 +1486,25 @@ static int process_cpuid(struct perf_file_section *section __maybe_unused,
>  	return ph->env.cpuid ? 0 : -ENOMEM;
>  }
>  
> +static int process_cpu_attributes(struct perf_file_section *section __maybe_unused,
> +				  struct perf_header *ph, int fd,
> +				  void *data __maybe_unused)
> +{
> +	ssize_t ret;
> +	u64 nr;
> +
> +	ret = readn(fd, &nr, sizeof(nr));
> +	if (ret != sizeof(nr))
> +		return -1;

you need to ensure backward compatibility, like new perf with
this section extended will be able to read old (current)
perf.data file.. and the other way round probably too

adding a identifier 'tag' for each value might do it

jirka
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