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?
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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