linux-kernel - Re: [PATCH] perf mmap: Discard head in overwrite_rb_find

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Date:   Wed, 7 Mar 2018 11:21:57 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Yisheng Xie <xieyisheng1@...wei.com>
Cc:     acme@...hat.com, mingo@...hat.com, peterz@...radead.org,
        namhyung@...nel.org, alexander.shishkin@...ux.intel.com,
        linux-kernel@...r.kernel.org, Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [PATCH] perf mmap: Discard head in overwrite_rb_find_range

On Tue, Mar 06, 2018 at 07:44:23PM +0800, Yisheng Xie wrote:
> In overwrite mode, start will be set to head in perf_mmap__read_init.
> Therefore, it is no need to set the start one more in
> overwrite_rb_find_range and *start can be used as head instead of
> passing head to overwrite_rb_find_range.

it conflicts a little with recent cleanup from Kan Liang,,
  https://marc.info/?t=152035082800001&r=1&w=2

otherwise it looks ok to me

jirka

> 
> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
> ---
>  tools/perf/util/mmap.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index 91531a7..6751ac9 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -223,19 +223,18 @@ int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd)
>  	return 0;
>  }
>  
> -static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)
> +static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
>  {
>  	struct perf_event_header *pheader;
> -	u64 evt_head = head;
> +	u64 evt_head = *start;
>  	int size = mask + 1;
>  
> -	pr_debug2("overwrite_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
> -	pheader = (struct perf_event_header *)(buf + (head & mask));
> -	*start = head;
> +	pr_debug2("%s: buf=%p, start=%"PRIx64"\n", __func__, buf, *start);
> +	pheader = (struct perf_event_header *)(buf + (*start & mask));
>  	while (true) {
> -		if (evt_head - head >= (unsigned int)size) {
> +		if (evt_head - *start >= (unsigned int)size) {
>  			pr_debug("Finished reading overwrite ring buffer: rewind\n");
> -			if (evt_head - head > (unsigned int)size)
> +			if (evt_head - *start > (unsigned int)size)
>  				evt_head -= pheader->size;
>  			*end = evt_head;
>  			return 0;
> @@ -287,7 +286,7 @@ int perf_mmap__read_init(struct perf_mmap *md, bool overwrite,
>  		 * Backward ring buffer is full. We still have a chance to read
>  		 * most of data from it.
>  		 */
> -		if (overwrite_rb_find_range(data, md->mask, head, startp, endp))
> +		if (overwrite_rb_find_range(data, md->mask, startp, endp))
>  			return -EINVAL;
>  	}
>  
> -- 
> 1.7.12.4
>