tasks blocking

Joel Sherrill joel.sherrill at OARcorp.com
Mon Dec 3 19:50:22 UTC 2001

Ilya Alexeev wrote:
> Hi RTEMS users & developers.
> Some time ago I wrote a similar letter but I have not received any answer so
> far.
> I am using gen68360 bsp & rtems-ss-20011025
> and I have noticed the following problem:
> When creating a task with RTEMS_INTERRUPT_LEVEL which is less than the
> interrupt level of the Periodic Interrup Timer (PIT), then after calling
> the directive rtems_task_wake_after this task may not wake up, the
> probability being very high.

I can't speak to PIT problems.  But I can speak to something later
which is probably confusing your interpretation.

> Here are the results of CPU_usage_Dump() after some time of testing.
> CPU Usage by thread
>    ID        NAME        TICKS
> 0x04010001   IDLE      11251
> 0x08010001   INIT       4523
> 0x08010002   TSK0        513
> 0x08010003   TSK1         31
> 0x08010004   TSK2        514
> 0x08010005   TSK3         37
> 0x08010006   TSK4         18
> 0x08010007   TSK5         18
> 0x08010008   TSK6         20
> 0x08010009   TSK7         32
> 0x0801000a   TSK8       6217
> 0x0801000b   TSK9        512
> Ticks since last reset = 5823
> Total Units = 23480
> As you see, some tasks have lost their control very quickly.

When a task executes for less than 1 clock tick quantum, it is
noted as having executed 1 tick anyway.  If you had a set of
tasks that did nothing but yield to one another in a tight loop,
then the "total units" would be much higher than "ticks since
last reset".

My reading of the above information is that you spend a lot of 
fractional time quantums in idle with INIT and TSK8 probably 
being the tasks that preempt IDLE on a regular basis.  

Without a way to record microsecond resolution, this is the
best you can reliably do.

> I will be glad to receive any replies and ideas.
> Ilya.

Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
Support Available                (256) 722-9985

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