Messages in this thread Patch in this message | | | Date | Thu, 5 May 2016 17:07:23 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH v2 3/4] perf tools: Support reading from backward ring buffer |
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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 <wangnan0@huawei.com> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Zefan Li <lizefan@huawei.com> > Cc: pi3orama@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 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
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