[Crash-utility] Re: [PATCH] Fix the "ps -m" command shows wrong duration of RU task

On 2025/05/07 16:16, HAGIO KAZUHITO(萩尾 一仁) wrote: > Hi, > > On 2025/04/28 19:38, Kenneth Yin wrote: >> The RU/TASK_RUNNING stat means the task is runnable. >> It is either currently running or on a run queue waiting to run. >> >> Currently, the crash tool uses the "rq_clock - sched_info->last_arrival" formula to >> calculate the duration of task in RU state. This is for the scenario of a task running on a CPU. > > The "ps -l" and "ps -m" options display what their help text describes, > not the duration of task in RU state. Please see "help ps". > > Also, tasks are sorted by the value, using different values for it could > make another confusion. > > The options have been used for a long time with the current code, if we > change the semantics of the options, it would be better to be careful. > The change might lose a kind of information instead of getting another > kind of information. > > On the other hand, I think that the duration of waiting in queue might > also be useful information. I'm not sure how we should display them, > but for example, how about adding a new option or adding a column for > last_queued? I thought of that the "runq" command might be suitable to display the waiting duration, because only tasks in the run queues have it. For example, extending the "runq -m" option or adding a new option. just my thought. Thanks, Kazu > > What do you think, folks? > > Thanks, > Kazu > >> >> But for the scenario of a task waiting in the CPU run queue (due to some reason >> for example cfs/rt queue throttled), this formula could cause misunderstanding. >> >> For example: >> [ 220 10:36:38.026] [RU] PID: 12345 TASK: ffff8d674ab6b180 CPU: 1 COMMAND: "task" >> >> Looking closer: >> >> crash> rq.clock ffff8de438a5acc0 >> clock = 87029229985307234, >> >> crash> task -R sched_info,se.exec_start >> PID: 12345 TASK: ffff8d674ab6b180 CPU: 1 COMMAND: "task" >> sched_info = { >> pcount = 33, >> run_delay = 0, >> last_arrival = 67983031958439673, >> last_queued = 87029224561119369 >> }, >> se.exec_start = 67983031958476937, >> >> 67983031 67983031 87029224 87029229 >> |<- running on CPU ->| <- IN ->|<- waiting in queue ->| >> >> For this scenario, the "task" was waiting in the run queue of the CPU only for 5 seconds, >> we should use the "rq_clock - sched_info->last_queued" formula.

>> >> We can trust sched_info->last_queued as it is only set when the task enters the CPU run queue. >> Furthermore, when the task hits/runs on a CPU or dequeues the CPU run queue, it will be reset to 0. >> >> Therefore, my idea is simple: >> >> If a task in RU stat and sched_info->last_queued has value (!= 0), >> it means this task is waiting in the run queue, use "rq_clock - sched_info->last_queued". >> >> Otherwise, if a task in RU stat and sched_info->last_queued = 0 >> and sched_info->last_arrival has value (it must be), it means this task is running on the CPU, >> use "rq_clock - sched_info->last_arrival". >> >> Signed-off-by: Kenneth Yin <kyin(a)redhat.com&gt; >> --- >> defs.h | 1 + >> symbols.c | 2 ++ >> task.c | 21 +++++++++++++++------ >> 3 files changed, 18 insertions(+), 6 deletions(-) >> >> diff --git a/defs.h b/defs.h >> index 4cf169c..66f5ce4 100644 >> --- a/defs.h >> +++ b/defs.h >> @@ -1787,6 +1787,7 @@ struct offset_table { /* stash of commonly-used offsets */ >> long vcpu_struct_rq; >> long task_struct_sched_info; >> long sched_info_last_arrival; >> + long sched_info_last_queued; >> long page_objects; >> long kmem_cache_oo; >> long char_device_struct_cdev; >> diff --git a/symbols.c b/symbols.c >> index e30fafe..fb5035f 100644 >> --- a/symbols.c >> +++ b/symbols.c >> @@ -9930,6 +9930,8 @@ dump_offset_table(char *spec, ulong makestruct) >> OFFSET(sched_rt_entity_run_list)); >> fprintf(fp, " sched_info_last_arrival: %ld\n", >> OFFSET(sched_info_last_arrival)); >> + fprintf(fp, " sched_info_last_queued: %ld\n", >> + OFFSET(sched_info_last_queued)); >> fprintf(fp, " task_struct_thread_info: %ld\n", >> OFFSET(task_struct_thread_info)); >> fprintf(fp, " task_struct_stack: %ld\n", >> diff --git a/task.c b/task.c >> index 3bafe79..f5386ac 100644 >> --- a/task.c >> +++ b/task.c >> @@ -332,9 +332,12 @@ task_init(void) >> MEMBER_OFFSET_INIT(task_struct_last_run, "task_struct", "last_run"); >> MEMBER_OFFSET_INIT(task_struct_timestamp, "task_struct", "timestamp"); >> MEMBER_OFFSET_INIT(task_struct_sched_info, "task_struct", "sched_info"); >> - if (VALID_MEMBER(task_struct_sched_info)) >> + if (VALID_MEMBER(task_struct_sched_info)) { >> MEMBER_OFFSET_INIT(sched_info_last_arrival, >> "sched_info", "last_arrival"); >> + MEMBER_OFFSET_INIT(sched_info_last_queued, >> + "sched_info", "last_queued"); >> + } >> if (VALID_MEMBER(task_struct_last_run) || >> VALID_MEMBER(task_struct_timestamp) || >> VALID_MEMBER(sched_info_last_arrival)) { >> @@ -6035,7 +6038,7 @@ ulonglong >> task_last_run(ulong task) >> { >> ulong last_run; >> - ulonglong timestamp; >> + ulonglong timestamp,last_queued; >> >> timestamp = 0; >> fill_task_struct(task); >> @@ -6047,10 +6050,16 @@ task_last_run(ulong task) >> } else if (VALID_MEMBER(task_struct_timestamp)) >> timestamp = tt->last_task_read ? ULONGLONG(tt->task_struct + >> OFFSET(task_struct_timestamp)) : 0; >> - else if (VALID_MEMBER(sched_info_last_arrival)) >> - timestamp = tt->last_task_read ? ULONGLONG(tt->task_struct + >> - OFFSET(task_struct_sched_info) + >> - OFFSET(sched_info_last_arrival)) : 0; >> + else if (VALID_MEMBER(sched_info_last_queued)) >> + last_queued = ULONGLONG(tt->task_struct + >> + OFFSET(task_struct_sched_info) + >> + OFFSET(sched_info_last_queued)); >> + if (last_queued != 0) { >> + timestamp = tt->last_task_read ? last_queued : 0; >> + } else if (VALID_MEMBER(sched_info_last_arrival)) >> + timestamp = tt->last_task_read ? ULONGLONG(tt->task_struct + >> + OFFSET(task_struct_sched_info) + >> + OFFSET(sched_info_last_arrival)) : 0; >> >> return timestamp; >> } > -- > Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io > To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io > https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/ > Contribution Guidelines: https://github.com/crash-utility/crash/wiki -- Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/ Contribution Guidelines: https://github.com/crash-utility/crash/wiki