linux-kernel - Re: [PATCH v2 2/4] perf record: implement -z=<level> and --mmap-flush=<thres> options

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Date:   Tue, 12 Feb 2019 14:08:34 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] perf record: implement -z=<level> and
 --mmap-flush=<thres> options

On Mon, Feb 11, 2019 at 11:22:38PM +0300, Alexey Budankov wrote:

SNIP

>  static void record__init_features(struct record *rec)
> @@ -838,6 +881,9 @@ static void record__init_features(struct record *rec)
>  	if (!(rec->opts.use_clockid && rec->opts.clockid_res_ns))
>  		perf_header__clear_feat(&session->header, HEADER_CLOCKID);
>  
> +	if (!record__comp_enabled(rec))
> +		perf_header__clear_feat(&session->header, HEADER_COMPRESSED);
> +
>  	perf_header__clear_feat(&session->header, HEADER_STAT);
>  }
>  
> @@ -1147,6 +1193,10 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>  	fd = perf_data__fd(data);
>  	rec->session = session;
>  
> +	rec->opts.comp_level = 0;
> +	session->header.env.comp_level = rec->opts.comp_level;
> +	session->header.env.comp_type = PERF_COMP_NONE;

hum I think both record and session are zerod from start,
so this seems superfluous

SNIP

> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index dec6d218c31c..5ad3a27a042f 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1463,6 +1463,21 @@ static int write_mem_topology(struct feat_fd *ff __maybe_unused,
>  	return ret;
>  }
>  
> +static int write_compressed(struct feat_fd *ff __maybe_unused,
> +			    struct perf_evlist *evlist __maybe_unused)
> +{
> +	int ret;
> +	u64 compression_info = ((u64)ff->ph->env.comp_type  << 32) | ff->ph->env.comp_level;
> +
> +	ret = do_write(ff, &compression_info, sizeof(compression_info));
> +	if (ret)
> +		return ret;
> +
> +	compression_info = ((u64)ff->ph->env.comp_ratio << 32) | ff->ph->env.comp_mmap_len;

let's not complicate this, if you have two u32 values
to store, store two u32 values ;-)

also please add version in case we will add new fields in the future,
so we can stay backward compatible

jirka