linux-kernel - Re: [PATCH V3 08/12] perf top: check per event overwrite term

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Date:   Thu, 11 Jan 2018 15:25:49 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...el.com
Cc:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, wangnan0@...wei.com,
        jolsa@...nel.org, namhyung@...nel.org, ak@...ux.intel.com,
        yao.jin@...ux.intel.com
Subject: Re: [PATCH V3 08/12] perf top: check per event overwrite term

On Thu, Dec 21, 2017 at 10:08:50AM -0800, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> Per event overwrite term is not forbidden in perf top, which can bring
> problems. Because perf top only support non-overwrite mode.
> 
> Check and forbid inconsistent per event overwrite term in the evlist.
> Make it possible to support either non-overwrite or overwrite mode.
> The overwrite mode is forbidden now, which will be removed when the
> overwrite mode is supported later.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/builtin-top.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
> 
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index c6ccda5..4b85e7b 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -881,6 +881,56 @@ static void perf_top__mmap_read(struct perf_top *top)
>  		perf_top__mmap_read_idx(top, i);
>  }
>  
> +/*
> + * Check per event overwrite term.
> + * perf top supports consistent mode for all events.
> + * Return -1 if the per event terms set but not consistent.

please list the rules for overwrite in the comment
are they just top specific?

SNIP

> +			if (evsel == perf_evlist__first(evlist))
> +				overwrite = set;
> +			else
> +				return -1;
> +		}
> +	}
> +
> +	if ((overwrite >= 0) && (opts->overwrite != overwrite))
> +		opts->overwrite = overwrite;
> +
> +	return 0;
> +}
> +
>  static int perf_top__start_counters(struct perf_top *top)
>  {
>  	char msg[BUFSIZ];
> @@ -890,6 +940,16 @@ static int perf_top__start_counters(struct perf_top *top)
>  
>  	perf_evlist__config(evlist, opts, &callchain_param);

so perf_evlist__config uses opts->overwrite, which you set
in your perf_top_overwrite_check call.. I'd think you need
to call it sooner

jirka