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Subject[PATCH v2 -perf/core 1/2] perf mmap: Discard head in overwrite_rb_find_range
Date
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.

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;
}

--
1.7.12.4
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