On Wed, Nov 19, 2025 at 9:29 PM Ian Rogers <[email protected]> wrote: > > On Wed, Nov 19, 2025 at 6:11 PM Namhyung Kim <[email protected]> wrote: > > > > It's possible that some kernel samples don't have matching deferred > > callchain records when the profiling session was ended before the > > threads came back to userspace. Let's flush the samples before > > finish the session. > > > > Also 32-bit systems can see partial mmap for the data. In that case, > > deferred samples won't point to the correct data once the mapping moves > > to the next portion of the file. Copy the original sample before it > > unmaps the current data. > > I think it is simpler to always copy. We may have events from > synthesis, inject, .. and not the reader. Relying on callers to know > that someone made a copy of the event and to make a defensive copy on > their behalf just feels error prone. > > In the python session API I need to deal with the lifetime of events. > Currently the events are copied: > https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/python.c?h=perf-tools-next#n507 > and I'm doing this for session tool callbacks: > https://lore.kernel.org/lkml/[email protected]/ > I think it can be made lazier by knowing the tool callback can assume > the event and sample are valid. We can delay the copying of the > event/sample for if the pyevent has a reference count >1 and we're > returning out of the tool callback. Doing some kind of global > knowledge in the reader for maintaining the correctness of memory, I'm > just not clear on how to make it always work.
I believe we always reuse the memory for the event, per event, in pipe mode: https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/session.c?h=perf-tools-next#n1868 so a lazy copy will be broken for the pipe mode case. Thanks, Ian > > Signed-off-by: Namhyung Kim <[email protected]> > > --- > > tools/perf/util/session.c | 98 +++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 98 insertions(+) > > > > diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c > > index 2e777fd1bcf6707b..b781e01ddcb4876b 100644 > > --- a/tools/perf/util/session.c > > +++ b/tools/perf/util/session.c > > @@ -1288,8 +1288,13 @@ static int evlist__deliver_sample(struct evlist > > *evlist, const struct perf_tool > > struct deferred_event { > > struct list_head list; > > union perf_event *event; > > + bool allocated; > > }; > > > > +/* > > + * This is called when a deferred callchain record comes up. Find all > > matching > > + * samples, merge the callchains and process them. > > + */ > > static int evlist__deliver_deferred_samples(struct evlist *evlist, > > const struct perf_tool *tool, > > union perf_event *event, > > @@ -1331,6 +1336,86 @@ static int evlist__deliver_deferred_samples(struct > > evlist *evlist, > > free(orig_sample.callchain); > > > > list_del(&de->list); > > + if (de->allocated) > > + free(de->event); > > + free(de); > > + > > + if (ret) > > + break; > > + } > > + return ret; > > +} > > + > > +/* > > + * This is called when the backing mmap is about to go away. It needs to > > save > > + * the original sample data until it finds the matching deferred > > callchains. > > + */ > > +static void evlist__copy_deferred_samples(struct evlist *evlist, > > + const struct perf_tool *tool, > > + struct machine *machine) > > +{ > > + struct deferred_event *de, *tmp; > > + struct evsel *evsel; > > + int ret = 0; > > + > > + list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) { > > + struct perf_sample sample; > > + size_t sz = de->event->header.size; > > + void *buf; > > + > > + if (de->allocated) > > + continue; > > + > > + buf = malloc(sz); > > + if (buf) { > > + memcpy(buf, de->event, sz); > > + de->event = buf; > > + de->allocated = true; > > + continue; > > + } > > + > > + /* The allocation failed, flush the sample now */ > > + ret = evlist__parse_sample(evlist, de->event, &sample); > > + if (ret == 0) { > > + evsel = evlist__id2evsel(evlist, sample.id); > > + evlist__deliver_sample(evlist, tool, de->event, > > + &sample, evsel, machine); > > + } > > + > > + list_del(&de->list); > > + BUG_ON(de->allocated); > > + free(de); > > + } > > +} > > + > > +/* > > + * This is called at the end of the data processing for the session. > > Flush the > > + * remaining samples as there's no hope for matching deferred callchains. > > + */ > > +static int evlist__flush_deferred_samples(struct evlist *evlist, > > + const struct perf_tool *tool, > > + struct machine *machine) > > +{ > > + struct deferred_event *de, *tmp; > > + struct evsel *evsel; > > + int ret = 0; > > + > > + list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) { > > + struct perf_sample sample; > > + > > + ret = evlist__parse_sample(evlist, de->event, &sample); > > + if (ret < 0) { > > + pr_err("failed to parse original sample\n"); > > + break; > > + } > > + > > + evsel = evlist__id2evsel(evlist, sample.id); > > + ret = evlist__deliver_sample(evlist, tool, de->event, > > + &sample, evsel, machine); > > + > > + list_del(&de->list); > > + if (de->allocated) > > + free(de->event); > > free(de); > > > > if (ret) > > @@ -1374,6 +1459,7 @@ static int machines__deliver_event(struct machines > > *machines, > > return -ENOMEM; > > > > de->event = event; > > + de->allocated = false; > > list_add_tail(&de->list, &evlist->deferred_samples); > > return 0; > > } > > @@ -2218,6 +2304,8 @@ reader__mmap(struct reader *rd, struct perf_session > > *session) > > } > > > > if (mmaps[rd->mmap_idx]) { > > + evlist__copy_deferred_samples(session->evlist, > > session->tool, > > + &session->machines.host); > > munmap(mmaps[rd->mmap_idx], rd->mmap_size); > > mmaps[rd->mmap_idx] = NULL; > > } > > @@ -2372,6 +2460,11 @@ static int __perf_session__process_events(struct > > perf_session *session) > > if (err) > > goto out_err; > > err = auxtrace__flush_events(session, tool); > > + if (err) > > + goto out_err; > > + err = evlist__flush_deferred_samples(session->evlist, > > + session->tool, > > + &session->machines.host); > > if (err) > > goto out_err; > > err = perf_session__flush_thread_stacks(session); > > @@ -2494,6 +2587,11 @@ static int __perf_session__process_dir_events(struct > > perf_session *session) > > if (ret) > > goto out_err; > > > > + ret = evlist__flush_deferred_samples(session->evlist, tool, > > + &session->machines.host); > > + if (ret) > > + goto out_err; > > + > > ret = perf_session__flush_thread_stacks(session); > > out_err: > > ui_progress__finish(); > > -- > > 2.52.0.rc1.455.g30608eb744-goog > >
