perf mmap: Discard head in overwrite_rb_find_range()

In overwrite mode, start will be set to head in perf_mmap__read_init().
Therefore, there is no need to set the start one more time 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>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1520944274-37001-1-git-send-email-xieyisheng1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 074c4fd..38ca3ff 100644 (file)
--- 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;
        }