linux-kernel - Re: [PATCH V3 04/12] perf mmap: introduce perf_mmap__read

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Message-ID: <20180111142541.GC16655@krava>
Date:   Thu, 11 Jan 2018 15:25:41 +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 04/12] perf mmap: introduce perf_mmap__read_done

On Thu, Dec 21, 2017 at 10:08:46AM -0800, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> The direction of overwrite mode is backward. The last mmap__read_event
> will set tail to map->prev. Need to correct the map->prev to head which
> is the end of next read.
> 
> It will be used later.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/util/mmap.c | 11 +++++++++++
>  tools/perf/util/mmap.h |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index a844a2f..4aaeb64 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -343,3 +343,14 @@ int perf_mmap__push(struct perf_mmap *md, bool overwrite,
>  out:
>  	return rc;
>  }
> +
> +/*
> + * Mandatory for overwrite mode
> + * The direction of overwrite mode is backward.
> + * The last mmap__read_event will set tail to map->prev.

you mean perf_mmap__read function in this comment, right?

jirka

> + * Need to correct the map->prev to head which is the end of next read.
> + */
> +void perf_mmap__read_done(struct perf_mmap *map)
> +{
> +	map->prev = perf_mmap__read_head(map);
> +}
> diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
> index abe9b9f..2df27c1 100644
> --- a/tools/perf/util/mmap.h
> +++ b/tools/perf/util/mmap.h
> @@ -96,4 +96,5 @@ size_t perf_mmap__mmap_len(struct perf_mmap *map);
>  
>  int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
>  			 u64 *start, u64 *end);
> +void perf_mmap__read_done(struct perf_mmap *map);
>  #endif /*__PERF_MMAP_H */
> -- 
> 2.5.5
>