Messages in this thread | | | Date | Tue, 22 Apr 2014 21:50:17 +0200 | Subject | Re: [PATCH] perf tools: fix processing of pid/tid for mmap records | From | Stephane Eranian <> |
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On Tue, Apr 22, 2014 at 9:40 PM, Don Zickus <dzickus@redhat.com> wrote: > On Mon, Apr 21, 2014 at 06:06:55PM +0200, Stephane Eranian wrote: >> perf tools: fix processing of pid/tid for mmap records >> >> Mmaps are global to a process (always). Processing them >> per-thread was causing some serious issues in case mmaps >> would overlap. The overlap fixups would only occur in the >> context of the thread which generated the overlapping >> mmap. But that was cause issues later on when a sample >> from another thread would fall into that overlapping >> mmap. > > eh? You are basically reverting my patch for a similar problem. :-) > > I was running a large multi-threading program (specjbb) and the threads > were not being seperated into their own map'd areas. So either I had to > lump all threads in to the same pid space or make the change you are > reverting. > I don't understand your problem. The address space is shared by ALL threads of a process. The mmaps are always shared by all threads?
> The problem I had with the double pid (as you propose), I would later look > up samples based on pid/tid and there would be _no_ map available because > it was created as a pid/pid pair. As a result, our c2c program would drop > thousands of samples on the floor (because there was no mapping for the > data address to get the major/minor/inode info).
That is your problem. You should only lookup mapping baseds on pid only not pid/tid. Why do you need tid?
> > Now I modified our c2c program to lookup samples as pid/pid but now the > maps lost tid info, and I had to hack around that by carrying the tid info > in a private struct. > If you need the tid, then it is okay to carry it on the side. I believe mmap lookups should ONLY use pid. That is how the address space of a process is contructed.
> Hopefully Jiri's thread work using pointers will solve both our problems. > :-) But I can't ack your patch because it will break my work :-( > > Cheers, > Don > > >> >> The solution to the problem is to handle ALL mmaps as >> occurring in the master thread (pid = tid) and then to >> lookup for thread map using pid as the tid argument. >> This is how samples are looking up for the thread map >> already (notice pid passed twice): >> >> int perf_event__preprocess_sample(const union perf_event *event, >> struct machine *machine, >> struct addr_location *al, >> struct perf_sample *sample) >> { >> struct thread *thread = machine__findnew_thread(machine, sample->pid, >> sample->pid); >> } >> >> Without this fix, some samples in overlapping regions >> may not be symbolized. >> >> Signed-off-by: Stephane Eranian <eranian@google.com> >> >> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c >> index a53cd0b..43cdc0a 100644 >> --- a/tools/perf/util/machine.c >> +++ b/tools/perf/util/machine.c >> @@ -1025,9 +1025,9 @@ int machine__process_mmap2_event(struct machine *machine, >> goto out_problem; >> return 0; >> } >> - >> + /* only look by pid for mmap events */ >> thread = machine__findnew_thread(machine, event->mmap2.pid, >> - event->mmap2.tid); >> + event->mmap2.pid); >> if (thread == NULL) >> goto out_problem; >> >> @@ -1073,9 +1073,9 @@ int machine__process_mmap_event(struct machine *machine, union perf_event *event >> goto out_problem; >> return 0; >> } >> - >> + /* only look by pid for mmap events */ >> thread = machine__findnew_thread(machine, event->mmap.pid, >> - event->mmap.tid); >> + event->mmap.pid); >> if (thread == NULL) >> goto out_problem; >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/
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