perf_evlist__mmap_read_backward() is introduced for reading backward
ring buffer. Different from reading forward, before reading, caller
needs to call perf_evlist__mmap_read_catchup() first.
Backward ring buffer should be read from 'head' pointer, not '0'.
perf_evlist__mmap_read_catchup() saves 'head' to 'md->prev', then
make it remember the start position after each reading.
Signed-off-by: Wang Nan <wangn...@huawei.com>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Zefan Li <lize...@huawei.com>
Cc: pi3or...@163.com
---
tools/perf/util/evlist.c | 39 +++++++++++++++++++++++++++++++++++++++
tools/perf/util/evlist.h | 4 ++++
2 files changed, 43 insertions(+)
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index f680983..b0f1d8f 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -767,6 +767,45 @@ union perf_event *perf_evlist__mmap_read(struct
perf_evlist *evlist, int idx)
head, &md->prev);
}
+union perf_event *
+perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx)
+{
+ struct perf_mmap *md = &evlist->mmap[idx];
+ u64 head, end;
+ u64 start = md->prev;
+
+ /*
+ * Check if event was unmapped due to a POLLHUP/POLLERR.
+ */
+ if (!atomic_read(&md->refcnt))
+ return NULL;
+
+ /* NOTE: head is negative in this case */
+ head = perf_mmap__read_head(md);
+
+ if (!head)
+ return NULL;
+
+ end = head + md->mask + 1;
+
+ if ((end - head) > -head)
+ end = 0;
+
+ return __perf_evlist__mmap_read(md, false, start, end, &md->prev);
+}
+
+void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx)
+{
+ struct perf_mmap *md = &evlist->mmap[idx];
+ u64 head;
+
+ if (!atomic_read(&md->refcnt))
+ return;
+
+ head = perf_mmap__read_head(md);
+ md->prev = head;
+}
+
static bool perf_mmap__empty(struct perf_mmap *md)
{
return perf_mmap__read_head(md) == md->prev && !md->auxtrace_mmap.base;
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 208897a..85d1b59 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -129,6 +129,10 @@ struct perf_sample_id *perf_evlist__id2sid(struct
perf_evlist *evlist, u64 id);
union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx);
+union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist,
+ int idx);
+void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx);
+
void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx);
int perf_evlist__open(struct perf_evlist *evlist);
--
1.8.3.4
