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 <k...@redhat.com>
>> ---
>> 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;
>> }
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