linux-kernel - Re: [PATCH 7/7] perf tools: Refine perf_mmap__read

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Date:   Mon, 5 Mar 2018 23:25:02 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
        namhyung@...nel.org, wangnan0@...wei.com, ak@...ux.intel.com
Subject: Re: [PATCH 7/7] perf tools: Refine perf_mmap__read_init

On Mon, Mar 05, 2018 at 02:10:59PM -0500, kan.liang@...ux.intel.com wrote:

SNIP

> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index e3921ed..403c5e6 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -235,16 +235,13 @@ static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u6
>  /*
>   * Report the start and end of the available data in ringbuffer
>   */
> -int perf_mmap__read_init(struct perf_mmap *md, bool overwrite,
> -			 u64 *startp, u64 *endp)
> +int perf_mmap__read_init(struct perf_mmap *md, bool overwrite)
>  {
>  	u64 head = perf_mmap__read_head(md);
>  	u64 old = md->prev;
>  	unsigned char *data = md->base + page_size;
>  	unsigned long size;
>  
> -	*startp = overwrite ? head : old;
> -	*endp = overwrite ? old : head;
>  	md->overwrite = overwrite;

hum, can't we set 'overwrite' at the moment we create struct perf_mmap?

it's not changing during the mmap's lifetime.. maybe we could do it in
perf_evlist__alloc_mmap function

really nice cleanup!

thanks,
jirka