On Tue, Feb 13, 2024 at 10:37 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> Commit 91e467bc568f ("perf machine: Use hashtable for machine
> threads") made the iteration of thread tids unordered. The perf report
> --tasks output now shows child threads in an order determined by the
> hashing. For example, in this snippet tid 3 appears after tid 256 even
> though they have the same ppid 2:
>
> ```
> $ perf report --tasks
> % pid tid ppid comm
> 0 0 -1 |swapper
> 2 2 0 | kthreadd
> 256 256 2 | kworker/12:1H-k
> 693761 693761 2 | kworker/10:1-mm
> 1301762 1301762 2 | kworker/1:1-mm_
> 1302530 1302530 2 | kworker/u32:0-k
> 3 3 2 | rcu_gp
> ...
> ```
>
> The output is easier to read if threads appear numerically
> increasing. To allow for this, read all threads into a list then sort
> with a comparator that orders by the child task's of the first common
> parent. The list creation and deletion are created as utilities on
> machine. The indentation is possible by counting the number of
> parents a child has.
>
> With this change the output for the same data file is now like:
> ```
> $ perf report --tasks
> % pid tid ppid comm
> 0 0 -1 |swapper
> 1 1 0 | systemd
> 823 823 1 | systemd-journal
> 853 853 1 | systemd-udevd
> 3230 3230 1 | systemd-timesyn
> 3236 3236 1 | auditd
> 3239 3239 3236 | audisp-syslog
> 3321 3321 1 | accounts-daemon
> ...
> ```
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
> tools/perf/builtin-report.c | 203 ++++++++++++++++++++----------------
> tools/perf/util/machine.c | 30 ++++++
> tools/perf/util/machine.h | 10 ++
> 3 files changed, 155 insertions(+), 88 deletions(-)
>
> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> index 8e16fa261e6f..b48f1d5309e3 100644
> --- a/tools/perf/builtin-report.c
> +++ b/tools/perf/builtin-report.c
> @@ -59,6 +59,7 @@
> #include <linux/ctype.h>
> #include <signal.h>
> #include <linux/bitmap.h>
> +#include <linux/list_sort.h>
> #include <linux/string.h>
> #include <linux/stringify.h>
> #include <linux/time64.h>
> @@ -828,35 +829,6 @@ static void tasks_setup(struct report *rep)
> rep->tool.no_warn = true;
> }
>
> -struct task {
> - struct thread *thread;
> - struct list_head list;
> - struct list_head children;
> -};
> -
> -static struct task *tasks_list(struct task *task, struct machine *machine)
> -{
> - struct thread *parent_thread, *thread = task->thread;
> - struct task *parent_task;
> -
> - /* Already listed. */
> - if (!list_empty(&task->list))
> - return NULL;
> -
> - /* Last one in the chain. */
> - if (thread__ppid(thread) == -1)
> - return task;
> -
> - parent_thread = machine__find_thread(machine, -1, thread__ppid(thread));
> - if (!parent_thread)
> - return ERR_PTR(-ENOENT);
> -
> - parent_task = thread__priv(parent_thread);
> - thread__put(parent_thread);
> - list_add_tail(&task->list, &parent_task->children);
> - return tasks_list(parent_task, machine);
> -}
> -
> struct maps__fprintf_task_args {
> int indent;
> FILE *fp;
> @@ -900,89 +872,144 @@ static size_t maps__fprintf_task(struct maps *maps, int indent, FILE *fp)
> return args.printed;
> }
>
> -static void task__print_level(struct task *task, FILE *fp, int level)
> +static int thread_level(struct machine *machine, const struct thread *thread)
> {
> - struct thread *thread = task->thread;
> - struct task *child;
> - int comm_indent = fprintf(fp, " %8d %8d %8d |%*s",
> - thread__pid(thread), thread__tid(thread),
> - thread__ppid(thread), level, "");
> + struct thread *parent_thread;
> + int res;
>
> - fprintf(fp, "%s\n", thread__comm_str(thread));
> + if (thread__tid(thread) <= 0)
> + return 0;
>
> - maps__fprintf_task(thread__maps(thread), comm_indent, fp);
> + if (thread__ppid(thread) <= 0)
> + return 1;
>
> - if (!list_empty(&task->children)) {
> - list_for_each_entry(child, &task->children, list)
> - task__print_level(child, fp, level + 1);
> + parent_thread = machine__find_thread(machine, -1, thread__ppid(thread));
> + if (!parent_thread) {
> + pr_err("Missing parent thread of %d\n", thread__tid(thread));
> + return 0;
> }
> + res = 1 + thread_level(machine, parent_thread);
> + thread__put(parent_thread);
> + return res;
> }
>
> -static int tasks_print(struct report *rep, FILE *fp)
> +static void task__print_level(struct machine *machine, struct thread *thread, FILE *fp)
> {
> - struct perf_session *session = rep->session;
> - struct machine *machine = &session->machines.host;
> - struct task *tasks, *task;
> - unsigned int nr = 0, itask = 0, i;
> - struct rb_node *nd;
> - LIST_HEAD(list);
> + int level = thread_level(machine, thread);
> + int comm_indent = fprintf(fp, " %8d %8d %8d |%*s",
> + thread__pid(thread), thread__tid(thread),
> + thread__ppid(thread), level, "");
>
> - /*
> - * No locking needed while accessing machine->threads,
> - * because --tasks is single threaded command.
> - */
> + fprintf(fp, "%s\n", thread__comm_str(thread));
>
> - /* Count all the threads. */
> - for (i = 0; i < THREADS__TABLE_SIZE; i++)
> - nr += machine->threads[i].nr;
> + maps__fprintf_task(thread__maps(thread), comm_indent, fp);
> +}
>
> - tasks = malloc(sizeof(*tasks) * nr);
> - if (!tasks)
> - return -ENOMEM;
> +static int task_list_cmp(void *priv, const struct list_head *la, const struct list_head *lb)
I'm a little afraid that this comparison logic becomes complex.
But I think it's better than having a tree of thread relationship.
Just a comment that explains why we need this would be nice.
> +{
> + struct machine *machine = priv;
> + struct thread_list *task_a = list_entry(la, struct thread_list, list);
> + struct thread_list *task_b = list_entry(lb, struct thread_list, list);
> + struct thread *a = task_a->thread;
> + struct thread *b = task_b->thread;
> + int level_a, level_b, res;
> +
> + /* Compare a and b to root. */
> + if (thread__tid(a) == thread__tid(b))
> + return 0;
>
> - for (i = 0; i < THREADS__TABLE_SIZE; i++) {
> - struct threads *threads = &machine->threads[i];
> + if (thread__tid(a) == 0)
> + return -1;
>
> - for (nd = rb_first_cached(&threads->entries); nd;
> - nd = rb_next(nd)) {
> - task = tasks + itask++;
> + if (thread__tid(b) == 0)
> + return 1;
>
> - task->thread = rb_entry(nd, struct thread_rb_node, rb_node)->thread;
> - INIT_LIST_HEAD(&task->children);
> - INIT_LIST_HEAD(&task->list);
> - thread__set_priv(task->thread, task);
> - }
> + /* If parents match sort by tid. */
> + if (thread__ppid(a) == thread__ppid(b)) {
> + return thread__tid(a) < thread__tid(b)
> + ? -1
> + : (thread__tid(a) > thread__tid(b) ? 1 : 0);
Can it be simply like this? We know tid(a) != tid(b).
return thread__tid(a) < thread__tid(b) ? -1 : 1;
> }
>
> /*
> - * Iterate every task down to the unprocessed parent
> - * and link all in task children list. Task with no
> - * parent is added into 'list'.
> + * Find a and b such that if they are a child of each other a and b's
> + * tid's match, otherwise a and b have a common parent and distinct
> + * tid's to sort by. First make the depths of the threads match.
> */
> - for (itask = 0; itask < nr; itask++) {
> - task = tasks + itask;
> -
> - if (!list_empty(&task->list))
> - continue;
> -
> - task = tasks_list(task, machine);
> - if (IS_ERR(task)) {
> - pr_err("Error: failed to process tasks\n");
> - free(tasks);
> - return PTR_ERR(task);
> + level_a = thread_level(machine, a);
> + level_b = thread_level(machine, b);
> + a = thread__get(a);
> + b = thread__get(b);
> + for (int i = level_a; i > level_b; i--) {
> + struct thread *parent = machine__find_thread(machine, -1, thread__ppid(a));
> +
> + thread__put(a);
> + if (!parent) {
> + pr_err("Missing parent thread of %d\n", thread__tid(a));
> + thread__put(b);
> + return -1;
> }
> + a = parent;
> + }
> + for (int i = level_b; i > level_a; i--) {
> + struct thread *parent = machine__find_thread(machine, -1, thread__ppid(b));
>
> - if (task)
> - list_add_tail(&task->list, &list);
> + thread__put(b);
> + if (!parent) {
> + pr_err("Missing parent thread of %d\n", thread__tid(b));
> + thread__put(a);
> + return 1;
> + }
> + b = parent;
> + }
> + /* Search up to a common parent. */
> + while (thread__ppid(a) != thread__ppid(b)) {
> + struct thread *parent;
> +
> + parent = machine__find_thread(machine, -1, thread__ppid(a));
> + thread__put(a);
> + if (!parent)
> + pr_err("Missing parent thread of %d\n", thread__tid(a));
> + a = parent;
> + parent = machine__find_thread(machine, -1, thread__ppid(b));
> + thread__put(b);
> + if (!parent)
> + pr_err("Missing parent thread of %d\n", thread__tid(b));
> + b = parent;
> + if (!a || !b)
> + return !a && !b ? 0 : (!a ? -1 : 1);
Wouldn't it leak a refcount if either a or b is NULL (not both)?
> + }
> + if (thread__tid(a) == thread__tid(b)) {
> + /* a is a child of b or vice-versa, deeper levels appear later. */
> + res = level_a < level_b ? -1 : (level_a > level_b ? 1 : 0);
> + } else {
> + /* Sort by tid now the parent is the same. */
> + res = thread__tid(a) < thread__tid(b) ? -1 : 1;
> }
> + thread__put(a);
> + thread__put(b);
> + return res;
> +}
> +
> +static int tasks_print(struct report *rep, FILE *fp)
> +{
> + struct machine *machine = &rep->session->machines.host;
> + LIST_HEAD(tasks);
> + int ret;
>
> - fprintf(fp, "# %8s %8s %8s %s\n", "pid", "tid", "ppid", "comm");
> + ret = machine__thread_list(machine, &tasks);
> + if (!ret) {
> + struct thread_list *task;
Do we really need this thread_list? Why not use an
array of threads directly?
Thanks,
Namhyung
>
> - list_for_each_entry(task, &list, list)
> - task__print_level(task, fp, 0);
> + list_sort(machine, &tasks, task_list_cmp);
>
> - free(tasks);
> - return 0;
> + fprintf(fp, "# %8s %8s %8s %s\n", "pid", "tid", "ppid", "comm");
> +
> + list_for_each_entry(task, &tasks, list)
> + task__print_level(machine, task->thread, fp);
> + }
> + thread_list__delete(&tasks);
> + return ret;
> }
>
> static int __cmd_report(struct report *rep)
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 3da92f18814a..7872ce92c9fc 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -3261,6 +3261,36 @@ int machines__for_each_thread(struct machines *machines,
> return rc;
> }
>
> +
> +static int thread_list_cb(struct thread *thread, void *data)
> +{
> + struct list_head *list = data;
> + struct thread_list *entry = malloc(sizeof(*entry));
> +
> + if (!entry)
> + return -ENOMEM;
> +
> + entry->thread = thread__get(thread);
> + list_add_tail(&entry->list, list);
> + return 0;
> +}
> +
> +int machine__thread_list(struct machine *machine, struct list_head *list)
> +{
> + return machine__for_each_thread(machine, thread_list_cb, list);
> +}
> +
> +void thread_list__delete(struct list_head *list)
> +{
> + struct thread_list *pos, *next;
> +
> + list_for_each_entry_safe(pos, next, list, list) {
> + thread__zput(pos->thread);
> + list_del(&pos->list);
> + free(pos);
> + }
> +}
> +
> pid_t machine__get_current_tid(struct machine *machine, int cpu)
> {
> if (cpu < 0 || (size_t)cpu >= machine->current_tid_sz)
> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> index 1279acda6a8a..b738ce84817b 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -280,6 +280,16 @@ int machines__for_each_thread(struct machines *machines,
> int (*fn)(struct thread *thread, void *p),
> void *priv);
>
> +struct thread_list {
> + struct list_head list;
> + struct thread *thread;
> +};
> +
> +/* Make a list of struct thread_list based on threads in the machine. */
> +int machine__thread_list(struct machine *machine, struct list_head *list);
> +/* Free up the nodes within the thread_list list. */
> +void thread_list__delete(struct list_head *list);
> +
> pid_t machine__get_current_tid(struct machine *machine, int cpu);
> int machine__set_current_tid(struct machine *machine, int cpu, pid_t pid,
> pid_t tid);
> --
> 2.43.0.687.g38aa6559b0-goog
>
