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SubjectRe: [PATCH v2 -perf/core 1/2] perf mmap: Discard head in overwrite_rb_find_range
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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@linux.intel.com>

Thanks,
Kan

> Signed-off-by: Yisheng Xie <xieyisheng1@huawei.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;
> }
>
>

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