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SubjectRe: [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@huawei.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
>

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