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 use it to remember the start position after each reading. Signed-off-by: Wang Nan <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Zefan Li <[email protected]> Cc: [email protected] --- tools/perf/util/evlist.c | 45 ++++++++++++++++++++++++++++++++++++++++++--- tools/perf/util/evlist.h | 4 ++++ 2 files changed, 46 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 119bf27..94d9085 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -680,14 +680,14 @@ static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist, } static union perf_event * -__perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head, - u64 old, u64 *prev) +__perf_evlist__mmap_read(struct perf_mmap *md, bool check_messup, + u64 head, u64 old, u64 *prev) { unsigned char *data = md->base + page_size; union perf_event *event = NULL; int diff = head - old; - if (overwrite) { + if (check_messup) { /* * If we're further behind than half the buffer, there's a chance * the writer will bite our tail and mess up the samples under us. @@ -766,6 +766,45 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx) old, &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, end, start, &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 a0d1522..7c10481 100644 --- a/tools/perf/util/evlist.h +++ b/tools/perf/util/evlist.h @@ -118,6 +118,10 @@ 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
