linux-kernel - Re: [PATCH V3 02/12] perf mmap: factor out function to find ringbuffer position

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Message-ID: <20180110153701.GA15442@krava>
Date:   Wed, 10 Jan 2018 16:37:01 +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 02/12] perf mmap: factor out function to find
 ringbuffer position

On Thu, Dec 21, 2017 at 10:08:44AM -0800, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> The perf record has specific codes to calculate the ringbuffer position
> for both overwrite and non-overwrite mode.
> The perf top will support both modes later.
> It is useful to make the specific codes generic.
> 
> Introduce a new interface perf_mmap__read_init() to find ringbuffer
> position.
> Add a check for map->refcnt in perf_mmap__read_init().
> 'size' is needed for both perf_mmap__read_init() and perf_mmap__push().
> Have to calculate in each function.

it's 2 separate changes then plus 1 not mentioned in changelog..
could you please split this into separate patches:

  - Introduce a new interface perf_mmap__read_init ...
  - Add a check for map->refcnt in perf_mmap__read_init
  - add new EAGAIN return value logic

thanks,
jirka

> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/util/mmap.c | 62 ++++++++++++++++++++++++++++++++++----------------
>  tools/perf/util/mmap.h |  2 ++
>  2 files changed, 45 insertions(+), 19 deletions(-)
> 
> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index 05076e6..3fd4f3c 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -267,41 +267,65 @@ static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u6
>  	return -1;
>  }
>  
> -int perf_mmap__push(struct perf_mmap *md, bool overwrite,
> -		    void *to, int push(void *to, void *buf, size_t size))
> +/*
> + * Report the start and end of the available data in ringbuffer
> + */
> +int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
> +			 u64 *start, u64 *end)
>  {
> -	u64 head = perf_mmap__read_head(md);
> -	u64 old = md->prev;
> -	u64 end = head, start = old;
> -	unsigned char *data = md->base + page_size;
> +	u64 head = perf_mmap__read_head(map);
> +	u64 old = map->prev;
> +	unsigned char *data = map->base + page_size;
>  	unsigned long size;
> -	void *buf;
> -	int rc = 0;
>  
> -	start = overwrite ? head : old;
> -	end = overwrite ? old : head;
> +	/*
> +	 * Check if event was unmapped due to a POLLHUP/POLLERR.
> +	 */
> +	if (!refcount_read(&map->refcnt))
> +		return -EINVAL;
>  
> -	if (start == end)
> -		return 0;
> +	*start = overwrite ? head : old;
> +	*end = overwrite ? old : head;
>  
> -	size = end - start;
> -	if (size > (unsigned long)(md->mask) + 1) {
> +	if (*start == *end)
> +		return -EAGAIN;
> +
> +	size = *end - *start;
> +	if (size > (unsigned long)(map->mask) + 1) {
>  		if (!overwrite) {
>  			WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");
>  
> -			md->prev = head;
> -			perf_mmap__consume(md, overwrite);
> -			return 0;
> +			map->prev = head;
> +			perf_mmap__consume(map, overwrite);
> +			return -EAGAIN;
>  		}
>  
>  		/*
>  		 * 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, &start, &end))
> -			return -1;
> +		if (overwrite_rb_find_range(data, map->mask, head, start, end))
> +			return -EINVAL;
>  	}
>  
> +	return 0;
> +}
> +
> +int perf_mmap__push(struct perf_mmap *md, bool overwrite,
> +		    void *to, int push(void *to, void *buf, size_t size))
> +{
> +	u64 head = perf_mmap__read_head(md);
> +	u64 end, start;
> +	unsigned char *data = md->base + page_size;
> +	unsigned long size;
> +	void *buf;
> +	int rc;
> +
> +	rc = perf_mmap__read_init(md, overwrite, &start, &end);
> +	if (rc < 0)
> +		return (rc == -EAGAIN) ? 0 : -1;
> +
> +	size = end - start;
>  	if ((start & md->mask) + size != (end & md->mask)) {
>  		buf = &data[start & md->mask];
>  		size = md->mask + 1 - (start & md->mask);
> diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
> index d640273..abe9b9f 100644
> --- a/tools/perf/util/mmap.h
> +++ b/tools/perf/util/mmap.h
> @@ -94,4 +94,6 @@ int perf_mmap__push(struct perf_mmap *md, bool backward,
>  
>  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);
>  #endif /*__PERF_MMAP_H */
> -- 
> 2.5.5
>