Em Wed, Apr 27, 2016 at 02:19:22AM +0000, Wang Nan escreveu:
> 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 <[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 | 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 17cd014..2e0b7b0 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -766,6 +766,45 @@ 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;
> +
> + /* NOTE: head is negative in this case */
What is this comment for, can you ellaborate? Are you double sure this
arithmetic with u64, negative values, that -head below are all ok?
I've applied the first two patches in this series.
I also need to check why we now need that catchup thing :-\
> + head = perf_mmap__read_head(md);
> +
> + if (!head)
> + return NULL;
> +
> + end = head + md->mask + 1;
> +
> + if ((end - head) > -head)
> + end = 0;
> +
> + 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 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
