linux-kernel - Re: [PATCH v2 -perf/core 1/2] perf mmap: Discard head in overwrite_rb_find

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Date:   Fri, 16 Mar 2018 10:16:53 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Yisheng Xie <xieyisheng1@...wei.com>, acme@...hat.com
Cc:     mingo@...hat.com, peterz@...radead.org, namhyung@...nel.org,
        jolsa@...hat.com, alexander.shishkin@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 -perf/core 1/2] perf mmap: Discard head in
 overwrite_rb_find_range



On 3/13/2018 8:31 AM, 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.
>

Looks good to me.

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan

> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
> ---
> v2:
>   - rebase to perf/core
> 
>   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 074c4fd..38ca3ff 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -199,19 +199,18 @@ 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;
> @@ -262,7 +261,7 @@ int perf_mmap__read_init(struct perf_mmap *md)
>   		 * 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, &md->start, &md->end))
> +		if (overwrite_rb_find_range(data, md->mask, &md->start, &md->end))
>   			return -EINVAL;
>   	}
>   
>