linux-kernel - Re: [PATCH v3] perf record: encode -k clockid frequency into Perf trace

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Message-ID: <20181008174212.GR3541@kernel.org>
Date:   Mon, 8 Oct 2018 14:42:12 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] perf record: encode -k clockid frequency into Perf
 trace

Em Wed, Oct 03, 2018 at 07:57:12PM +0300, Alexey Budankov escreveu:
> 
> Store -k clockid frequency into Perf trace to enable timestamps 
> derived metrics conversion into wall clock time on reporting stage.

<SNIP>

> +++ b/tools/perf/util/env.h
> @@ -63,6 +63,7 @@ struct perf_env {
>  	struct numa_node	*numa_nodes;
>  	struct memory_node	*memory_nodes;
>  	unsigned long long	 memory_bsize;
> +	size_t                   clockid_res_ns;
>  };
>  
>  extern struct perf_env perf_env;
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 1ec1d9bc2d63..4ce5339158f7 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1034,6 +1034,13 @@ static int write_auxtrace(struct feat_fd *ff,
>  	return err;
>  }
>  
> +static int write_clockid(struct feat_fd *ff,
> +			 struct perf_evlist *evlist __maybe_unused)
> +{
> +	return do_write(ff, &ff->ph->env.clockid_res_ns,
> +			sizeof(ff->ph->env.clockid_res_ns));
> +}
> +

Is sizeof(size_t) the same everywhere? I think you should encode this
always as a u64, read it, assign it to a temp u64 var, write the u64 to
the perf.data header, read it using do_read_u64, that will take care of
endianness, then set it to the size_t in the ff->ph->env.clockid_res_ns,
right?

I'm removing the patch till this gets sorted out,

Thanks,

- Arnaldo