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SubjectRe: [PATCH V3 04/12] perf mmap: introduce perf_mmap__read_done
Hello,

On Thu, Dec 21, 2017 at 10:08:46AM -0800, kan.liang@intel.com wrote:
> From: Kan Liang <kan.liang@intel.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.

Why do you update the map->prev needlessly then? I think we don't
need it for overwrite/backward mode, right?

Also I guess the current code might miss some events since the head
can be different between _read_init() and _read_done(), no?

Thanks,
Namhyung


>
> It will be used later.
>
> Signed-off-by: Kan Liang <kan.liang@intel.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.
> + * 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
>

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