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SubjectJiffy is not able to measure the fraction of time a process runs a processor
Hi all,

I am trying to measure the fraction of time a process runs on a
processor, but the jiffies is not able to provide an accurate value.

The example below shows that in one kernel tick or one jiffy, kmix
and lpd was schedule in the same processor and the cpu time of each
one was zero. The calculation of cpu time is based on jiffies and the
cpu time is zero because the jiffy value was not incremented yet.

PID : NAME : LAST ARRIVAL : CPU TIME : CALLER
4544 : kmix : 6170433 : 0
: work_resched+0x6c
4078 : lpd : 6170433 : 0
: __down_interruptible+0x5
4544 : kmix : 6170433 : 0
: schedule_timeout+0xb8


Look again, when jiffies is 6170503 klipper and emacs are scheduled
many times.

4534 : klipper : 6170503 : 0
: preempt_schedule_irq+0xb8
4534 : klipper : 6170503 : 0
: preempt_schedule+0x3d
4534 : klipper : 6170503 : 0
: work_resched+0x34
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: preempt_schedule+0x5
4534 : klipper : 6170503 : 0
: work_resched+0x34
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: work_resched+0x5
16150 : emacs : 6170503 : 0
: work_resched+0x5
16150 : emacs : 6170503 : 0
: work_resched+0x5
16150 : emacs : 6170503 : 0
: work_resched+0x5
16150 : emacs : 6170503 : 0
: preempt_schedule+0x5
16150 : emacs : 6170503 : 0
: schedule_timeout+0x34
4534 : klipper : 6170503 : 0
: preempt_schedule+0x6c
4534 : klipper : 6170503 : 0
: work_resched+0x34
4534 : klipper : 6170503 : 0
: work_resched+0x5
4534 : klipper : 6170503 : 0
: schedule_timeout+0x5

Does anyone know how can I measure precisely the fraction of time a
process runs on a processor?

BR,

Mauricio Lin.
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