Messages in this thread | | | Date | Sun, 4 Aug 2019 12:44:34 +0100 | From | John Keeping <> | Subject | Re: [PATCH 2/2] perf unwind: fix libunwind when tid != pid |
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On Fri, 2 Aug 2019 15:30:39 +0200 Jiri Olsa <jolsa@redhat.com> wrote:
> On Mon, Jul 29, 2019 at 06:24:30PM +0100, John Keeping wrote: > > Commit e5adfc3e7e77 ("perf map: Synthesize maps only for thread group > > leader") changed the recording side so that we no longer get mmap events > > for threads other than the thread group leader. > > > > When a file recorded after this change is loaded, the lack of mmap > > records mean that unwinding is not set up for any other threads. > > sry I dont' follow what's the problem here, could you please > describe the scenrio where the current code is failing in > more details
With perf compiled to use libunwind, run:
perf record --call-graph=dwarf -t $TID -- sleep 5 perf report
If $TID is a process, then the output has the call graph, but if it's a secondary thread then it is as if --no-call-graph was specified.
> > > > Following the rationale in that commit, move the libunwind fields into > > struct map_groups and update the libunwind functions to take this > > instead of the struct thread. This is only required for > > unwind__finish_access which must now be called from map_groups__delete > > and the others are changed for symmetry. > > > > Note that unwind__get_entries keeps the thread argument since it is > > required for symbol lookup and the libdw unwind provider uses the thread > > ID. > > SNIP > > > @@ -59,37 +59,31 @@ int unwind__prepare_access(struct thread *thread, struct map *map, > > return 0; > > } > > out_register: > > - unwind__register_ops(thread, ops); > > + unwind__register_ops(mg, ops); > > > > - err = thread->unwind_libunwind_ops->prepare_access(thread); > > + err = mg->unwind_libunwind_ops->prepare_access(mg); > > if (initialized) > > *initialized = err ? false : true; > > return err; > > } > > > > -void unwind__flush_access(struct thread *thread) > > +void unwind__flush_access(struct map_groups *mg) > > { > > - if (!dwarf_callchain_users) > > - return; > > why did you remove this check?
I don't think there is any way for unwind_libunwind_ops to be set if !dwarf_callchain_users so this is redundant given the following condition.
But this should probably be a separate patch.
> > - > > - if (thread->unwind_libunwind_ops) > > - thread->unwind_libunwind_ops->flush_access(thread); > > + if (mg->unwind_libunwind_ops) > > + mg->unwind_libunwind_ops->flush_access(mg); > > } > > > > -void unwind__finish_access(struct thread *thread) > > +void unwind__finish_access(struct map_groups *mg) > > { > > - if (!dwarf_callchain_users) > > - return; > > why did you remove this check?
Likewise.
Regards, John
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