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authorWang Nan <wangnan0@huawei.com>2016-05-09 01:47:50 +0000
committerArnaldo Carvalho de Melo <acme@redhat.com>2016-05-09 17:20:53 -0300
commite24c7520ea9c3e5bb51592c2134aafbf75a3f88a (patch)
treefe6c5e5e1f3ef7676b71a3e3b555a2a6a2647232
parentaff633406ca2772554bad7b37f2dfbc409b6ea74 (diff)
downloadlinux-e24c7520ea9c3e5bb51592c2134aafbf75a3f88a.tar.gz
perf tools: Support reading from backward ring buffer
perf_evlist__mmap_read_backward() is introduced for reading backward ring buffer. Since direction for reading such ring buffer is different from the direction kernel writing to it, and since user need to fetch most recent record from it, a perf_evlist__mmap_read_catchup() is introduced to move the reading pointer to the end of the buffer. Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Zefan Li <lizefan@huawei.com> Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1462758471-89706-2-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
-rw-r--r--tools/perf/util/evlist.c50
-rw-r--r--tools/perf/util/evlist.h4
2 files changed, 54 insertions, 0 deletions
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 17cd01421e7f..c4bfe11479a0 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -766,6 +766,56 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
return perf_mmap__read(md, evlist->overwrite, old, 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;
+
+ head = perf_mmap__read_head(md);
+ if (!head)
+ return NULL;
+
+ /*
+ * 'head' pointer starts from 0. Kernel minus sizeof(record) form
+ * it each time when kernel writes to it, so in fact 'head' is
+ * negative. 'end' pointer is made manually by adding the size of
+ * the ring buffer to 'head' pointer, means the validate data can
+ * read is the whole ring buffer. If 'end' is positive, the ring
+ * buffer has not fully filled, so we must adjust 'end' to 0.
+ *
+ * However, since both 'head' and 'end' is unsigned, we can't
+ * simply compare 'end' against 0. Here we compare '-head' and
+ * the size of the ring buffer, where -head is the number of bytes
+ * kernel write to the ring buffer.
+ */
+ if (-head < (u64)(md->mask + 1))
+ end = 0;
+ else
+ end = head + md->mask + 1;
+
+ return perf_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 208897a646ca..85d1b59802e8 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);