Re: [PATCH v2 13/13] perf machine thread: Remove exited threads by default
From: Ian Rogers
Date: Mon Oct 23 2023 - 14:49:22 EST
On Mon, Oct 23, 2023 at 7:24 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 12/10/23 09:23, Ian Rogers wrote:
> > struct thread values hold onto references to mmaps, dsos, etc. When a
> > thread exits it is necessary to clean all of this memory up by
> > removing the thread from the machine's threads. Some tools require
> > this doesn't happen, such as perf report if offcpu events exist or if
> > a task list is being generated, so add a symbol_conf value to make the
> > behavior optional. When an exited thread is left in the machine's
> > threads, mark it as exited.
> >
> > This change relates to commit 40826c45eb0b ("perf thread: Remove
> > notion of dead threads"). Dead threads were removed as they had a
> > reference count of 0 and were difficult to reason about with the
> > reference count checker. Here a thread is removed from threads when it
> > exits, unless via symbol_conf the exited thread isn't remove and is
> > marked as exited. Reference counting behaves as it normally does.
>
> Can we exclude AUX area tracing?
>
> Essentially, the EXIT event happens when the task is still running
> in kernel mode, so the thread has not in fact fully exited.
>
> Example:
>
> # perf record -a --kcore -e intel_pt// uname
>
> Before:
>
> # perf script --itrace=b --show-task-events -C6 | grep -C10 EXIT
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63124ee __perf_event_header__init_id+0x5e ([kernel.kallsyms]) => ffffffffb63124f7 __perf_event_header__init_id+0x67 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6312501 __perf_event_header__init_id+0x71 ([kernel.kallsyms]) => ffffffffb6312512 __perf_event_header__init_id+0x82 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6312531 __perf_event_header__init_id+0xa1 ([kernel.kallsyms]) => ffffffffb6316b3a perf_event_task_output+0x26a ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6316b40 perf_event_task_output+0x270 ([kernel.kallsyms]) => ffffffffb6316959 perf_event_task_output+0x89 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6316966 perf_event_task_output+0x96 ([kernel.kallsyms]) => ffffffffb6322040 perf_output_begin+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6322080 perf_output_begin+0x40 ([kernel.kallsyms]) => ffffffffb6194dc0 __rcu_read_lock+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6194de1 __rcu_read_lock+0x21 ([kernel.kallsyms]) => ffffffffb6322085 perf_output_begin+0x45 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63220ce perf_output_begin+0x8e ([kernel.kallsyms]) => ffffffffb611d280 preempt_count_add+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb611d2bf preempt_count_add+0x3f ([kernel.kallsyms]) => ffffffffb63220d3 perf_output_begin+0x93 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63220e8 perf_output_begin+0xa8 ([kernel.kallsyms]) => ffffffffb63220ff perf_output_begin+0xbf ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: PERF_RECORD_EXIT(14740:14740):(14739:14739)
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6322119 perf_output_begin+0xd9 ([kernel.kallsyms]) => ffffffffb6322128 perf_output_begin+0xe8 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6322146 perf_output_begin+0x106 ([kernel.kallsyms]) => ffffffffb63220ea perf_output_begin+0xaa ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63220f9 perf_output_begin+0xb9 ([kernel.kallsyms]) => ffffffffb63221ab perf_output_begin+0x16b ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63221ae perf_output_begin+0x16e ([kernel.kallsyms]) => ffffffffb63221b6 perf_output_begin+0x176 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6322202 perf_output_begin+0x1c2 ([kernel.kallsyms]) => ffffffffb6322167 perf_output_begin+0x127 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb632218c perf_output_begin+0x14c ([kernel.kallsyms]) => ffffffffb631696b perf_event_task_output+0x9b ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6316990 perf_event_task_output+0xc0 ([kernel.kallsyms]) => ffffffffb61034a0 __task_pid_nr_ns+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb61034b7 __task_pid_nr_ns+0x17 ([kernel.kallsyms]) => ffffffffb6194dc0 __rcu_read_lock+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6194de1 __rcu_read_lock+0x21 ([kernel.kallsyms]) => ffffffffb61034bc __task_pid_nr_ns+0x1c ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6103503 __task_pid_nr_ns+0x63 ([kernel.kallsyms]) => ffffffffb610353b __task_pid_nr_ns+0x9b ([kernel.kallsyms])
>
> After:
>
> $ perf script --itrace=b --show-task-events -C6 | grep -C10 EXIT
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63124ee __perf_event_header__init_id+0x5e ([kernel.kallsyms]) => ffffffffb63124f7 __perf_event_header__init_id+0x67 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6312501 __perf_event_header__init_id+0x71 ([kernel.kallsyms]) => ffffffffb6312512 __perf_event_header__init_id+0x82 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6312531 __perf_event_header__init_id+0xa1 ([kernel.kallsyms]) => ffffffffb6316b3a perf_event_task_output+0x26a ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6316b40 perf_event_task_output+0x270 ([kernel.kallsyms]) => ffffffffb6316959 perf_event_task_output+0x89 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6316966 perf_event_task_output+0x96 ([kernel.kallsyms]) => ffffffffb6322040 perf_output_begin+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6322080 perf_output_begin+0x40 ([kernel.kallsyms]) => ffffffffb6194dc0 __rcu_read_lock+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb6194de1 __rcu_read_lock+0x21 ([kernel.kallsyms]) => ffffffffb6322085 perf_output_begin+0x45 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63220ce perf_output_begin+0x8e ([kernel.kallsyms]) => ffffffffb611d280 preempt_count_add+0x0 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb611d2bf preempt_count_add+0x3f ([kernel.kallsyms]) => ffffffffb63220d3 perf_output_begin+0x93 ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: 1 branches: ffffffffb63220e8 perf_output_begin+0xa8 ([kernel.kallsyms]) => ffffffffb63220ff perf_output_begin+0xbf ([kernel.kallsyms])
> uname 14740 [006] 26795.092638: PERF_RECORD_EXIT(14740:14740):(14739:14739)
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6322119 perf_output_begin+0xd9 ([kernel.kallsyms]) => ffffffffb6322128 perf_output_begin+0xe8 ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6322146 perf_output_begin+0x106 ([kernel.kallsyms]) => ffffffffb63220ea perf_output_begin+0xaa ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb63220f9 perf_output_begin+0xb9 ([kernel.kallsyms]) => ffffffffb63221ab perf_output_begin+0x16b ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb63221ae perf_output_begin+0x16e ([kernel.kallsyms]) => ffffffffb63221b6 perf_output_begin+0x176 ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6322202 perf_output_begin+0x1c2 ([kernel.kallsyms]) => ffffffffb6322167 perf_output_begin+0x127 ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb632218c perf_output_begin+0x14c ([kernel.kallsyms]) => ffffffffb631696b perf_event_task_output+0x9b ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6316990 perf_event_task_output+0xc0 ([kernel.kallsyms]) => ffffffffb61034a0 __task_pid_nr_ns+0x0 ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb61034b7 __task_pid_nr_ns+0x17 ([kernel.kallsyms]) => ffffffffb6194dc0 __rcu_read_lock+0x0 ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6194de1 __rcu_read_lock+0x21 ([kernel.kallsyms]) => ffffffffb61034bc __task_pid_nr_ns+0x1c ([kernel.kallsyms])
> :14740 14740 [006] 26795.092638: 1 branches: ffffffffb6103503 __task_pid_nr_ns+0x63 ([kernel.kallsyms]) => ffffffffb610353b __task_pid_nr_ns+0x9b ([kernel.kallsyms])
>
> This will also affect samples made after PERF_RECORD_EXIT but before
> the task finishes exiting.
Makes sense. Would an appropriate fix be in perf_session__open to set:
symbol_conf.keep_exited_threads = true;
when:
perf_header__has_feat(&session->header, HEADER_AUXTRACE)
It is kind of hacky to be changing global state this way, but
symbol_conf is like that in general.
Thanks,
Ian
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> > tools/perf/builtin-report.c | 7 +++++++
> > tools/perf/util/machine.c | 10 +++++++---
> > tools/perf/util/symbol_conf.h | 3 ++-
> > tools/perf/util/thread.h | 14 ++++++++++++++
> > 4 files changed, 30 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index dcedfe00f04d..749246817aed 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -1411,6 +1411,13 @@ int cmd_report(int argc, const char **argv)
> > if (ret < 0)
> > goto exit;
> >
> > + /*
> > + * tasks_mode require access to exited threads to list those that are in
> > + * the data file. Off-cpu events are synthesized after other events and
> > + * reference exited threads.
> > + */
> > + symbol_conf.keep_exited_threads = true;
> > +
> > annotation_options__init(&report.annotation_opts);
> >
> > ret = perf_config(report__config, &report);
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index 6ca7500e2cf4..5cda47eb337d 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -2157,9 +2157,13 @@ int machine__process_exit_event(struct machine *machine, union perf_event *event
> > if (dump_trace)
> > perf_event__fprintf_task(event, stdout);
> >
> > - if (thread != NULL)
> > - thread__put(thread);
> > -
> > + if (thread != NULL) {
> > + if (symbol_conf.keep_exited_threads)
> > + thread__set_exited(thread, /*exited=*/true);
> > + else
> > + machine__remove_thread(machine, thread);
> > + }
> > + thread__put(thread);
> > return 0;
> > }
> >
> > diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h
> > index 2b2fb9e224b0..6040286e07a6 100644
> > --- a/tools/perf/util/symbol_conf.h
> > +++ b/tools/perf/util/symbol_conf.h
> > @@ -43,7 +43,8 @@ struct symbol_conf {
> > disable_add2line_warn,
> > buildid_mmap2,
> > guest_code,
> > - lazy_load_kernel_maps;
> > + lazy_load_kernel_maps,
> > + keep_exited_threads;
> > const char *vmlinux_name,
> > *kallsyms_name,
> > *source_prefix,
> > diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> > index e79225a0ea46..0df775b5c110 100644
> > --- a/tools/perf/util/thread.h
> > +++ b/tools/perf/util/thread.h
> > @@ -36,13 +36,22 @@ struct thread_rb_node {
> > };
> >
> > DECLARE_RC_STRUCT(thread) {
> > + /** @maps: mmaps associated with this thread. */
> > struct maps *maps;
> > pid_t pid_; /* Not all tools update this */
> > + /** @tid: thread ID number unique to a machine. */
> > pid_t tid;
> > + /** @ppid: parent process of the process this thread belongs to. */
> > pid_t ppid;
> > int cpu;
> > int guest_cpu; /* For QEMU thread */
> > refcount_t refcnt;
> > + /**
> > + * @exited: Has the thread had an exit event. Such threads are usually
> > + * removed from the machine's threads but some events/tools require
> > + * access to dead threads.
> > + */
> > + bool exited;
> > bool comm_set;
> > int comm_len;
> > struct list_head namespaces_list;
> > @@ -189,6 +198,11 @@ static inline refcount_t *thread__refcnt(struct thread *thread)
> > return &RC_CHK_ACCESS(thread)->refcnt;
> > }
> >
> > +static inline void thread__set_exited(struct thread *thread, bool exited)
> > +{
> > + RC_CHK_ACCESS(thread)->exited = exited;
> > +}
> > +
> > static inline bool thread__comm_set(const struct thread *thread)
> > {
> > return RC_CHK_ACCESS(thread)->comm_set;
>