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Date: Mon, 6 Nov 2023 13:28:43 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Ian Rogers <irogers@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Nick Terrell <terrelln@...com>,
Kan Liang <kan.liang@...ux.intel.com>,
Andi Kleen <ak@...ux.intel.com>,
Kajol Jain <kjain@...ux.ibm.com>,
Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
Huacai Chen <chenhuacai@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Vincent Whitchurch <vincent.whitchurch@...s.com>,
"Steinar H. Gunderson" <sesse@...gle.com>,
Liam Howlett <liam.howlett@...cle.com>,
Miguel Ojeda <ojeda@...nel.org>,
Colin Ian King <colin.i.king@...il.com>,
Dmitrii Dolgov <9erthalion6@...il.com>,
Yang Jihong <yangjihong1@...wei.com>,
Ming Wang <wangming01@...ngson.cn>,
James Clark <james.clark@....com>,
K Prateek Nayak <kprateek.nayak@....com>,
Sean Christopherson <seanjc@...gle.com>,
Leo Yan <leo.yan@...aro.org>,
Ravi Bangoria <ravi.bangoria@....com>,
German Gomez <german.gomez@....com>,
Changbin Du <changbin.du@...wei.com>,
Paolo Bonzini <pbonzini@...hat.com>, Li Dong <lidong@...o.com>,
Sandipan Das <sandipan.das@....com>,
liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4 05/53] perf machine thread: Remove exited threads by
default
On 2/11/23 19:56, 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 auxtrace events, 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.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
For auxtrace:
Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
> tools/perf/builtin-report.c | 7 +++++++
> tools/perf/util/machine.c | 10 +++++++---
> tools/perf/util/session.c | 5 +++++
> tools/perf/util/symbol_conf.h | 3 ++-
> tools/perf/util/thread.h | 14 ++++++++++++++
> 5 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> index 9cb1da2dc0c0..121a2781323c 100644
> --- a/tools/perf/builtin-report.c
> +++ b/tools/perf/builtin-report.c
> @@ -1426,6 +1426,13 @@ 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 90c750150b19..a985d004aa8d 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/session.c b/tools/perf/util/session.c
> index 1e9aa8ed15b6..c6afba7ab1a5 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -115,6 +115,11 @@ static int perf_session__open(struct perf_session *session, int repipe_fd)
> return -1;
> }
>
> + if (perf_header__has_feat(&session->header, HEADER_AUXTRACE)) {
> + /* Auxiliary events may reference exited threads, hold onto dead ones. */
> + symbol_conf.keep_exited_threads = true;
> + }
> +
> if (perf_data__is_pipe(data))
> 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;
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