[PATCH 44/46] perf record: Read from backward ring buffer

Wang Nan
2016-02-26T09:33:41Z

Introduce rb_find_range() to find start and end position from a backward
ring buffer.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
tools/perf/builtin-record.c | 69 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 67 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index eee3436..0ce7f52 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -87,6 +87,61 @@ static int process_synthesized_event(struct perf_tool *tool,
return record__write(rec, event, event->header.size);
}

+static int
+backward_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)
+{
+ struct perf_event_header *pheader;
+ u64 evt_head = head;
+ int size = mask + 1;
+
+ pr_debug2("backward_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
+ pheader = (struct perf_event_header *)(buf + (head & mask));
+ *start = head;
+ while (true) {
+ if (evt_head - head >= (unsigned int)size) {
+ pr_debug("Finshed reading backward ring buffer: rewind\n");
+ if (evt_head - head > (unsigned int)size)
+ evt_head -= pheader->size;
+ *end = evt_head;
+ return 0;
+ }
+
+ pheader = (struct perf_event_header *)(buf + (evt_head & mask));
+
+ if (pheader->size == 0) {
+ pr_debug("Finshed reading backward ring buffer: get start\n");
+ *end = evt_head;
+ return 0;
+ }
+
+ evt_head += pheader->size;
+ pr_debug3("move evt_head: %"PRIx64"\n", evt_head);
+ }
+ WARN_ONCE(1, "Shouldn't get here\n");
+ return -1;
+}
+
+static int
+rb_find_range(struct perf_evlist *evlist, int idx,
+ void *data, int mask, u64 head, u64 old,
+ u64 *start, u64 *end)
+{
+ int channel;
+
+ channel = perf_evlist__idx_channel(evlist, idx);
+ if (!perf_evlist__channel_check(evlist, channel, RDONLY)) {
+ *start = old;
+ *end = head;
+ return 0;
+ }
+
+ if (perf_evlist__channel_check(evlist, channel, BACKWARD))
+ return backward_rb_find_range(data, mask, head, start, end);
+
+ WARN_ONCE(1, "Unable to find start position from a read-only ring buffer\n");
+ return -1;
+}
+
static int record__mmap_read(struct record *rec, int idx)
{
struct perf_mmap *md = &rec->evlist->mmap[idx];
@@ -98,6 +153,10 @@ static int record__mmap_read(struct record *rec, int idx)
void *buf;
int rc = 0;

+ if (rb_find_range(rec->evlist, idx, data, md->mask, head,
+ old, &start, &end))
+ return -1;
+
if (start == end)
return 0;

@@ -531,8 +590,14 @@ static bool record__mmap_should_read(struct record *rec, int idx)
return false;
if (perf_evlist__channel_idx(rec->evlist, &channel, &idx))
return false;
- if (perf_evlist__channel_check(rec->evlist, channel, RDONLY))
- return false;
+ if (perf_evlist__channel_check(rec->evlist, channel, RDONLY)) {
+ if (rec->overwrite_evt_state != OVERWRITE_EVT_DATA_PENDING)
+ return false;
+ if (perf_evlist__channel_check(rec->evlist, channel, BACKWARD))
+ return true;
+ else
+ return false;
+ }
return true;
}

--
1.8.3.4