Re: [Xenomai] High CPU load using q_send under pSOS skin

[Philippe Gerum <rpm@xenomai.org>]

On 02/06/2014 06:26 PM, Philippe Gerum wrote:
> On 02/06/2014 05:25 PM, Marcel van Mierlo wrote:
>> Hi,
>>
>> I've been investigating this for a couple of days and would really
>> appreciate some insight
>> on what might be going on or what I can do to progress this...
>>
>> I am porting a legacy pSOS application - to Xenomai on BeagleBoard Black
>> 3.8 kernel
>> and have noticed %CPU (via. top) of MAIN around 40% when using q_send,
>> and doing no "work".
>>
>> Surprisingly,  if I add a printf() and fflush() to the task body then
>> the CPU drops down to < 1%.
>>
>> I've checked compile options, nothing obviously wrong. Here is the
>> (abridged) body of the task.
>> It just provides a periodic message for watchdog purposes.
>>
>>
>> [%CPU ~%40]
>> while{1}
>> {
>>      q_send(ulCanTQid, (INT32 *)&oCanMsg);
>>      tm_wkafter(100);  // ~100ms
>> }
>>
>>
>> [%CPU < %1]
>> while{1}
>> {
>>      q_send(ulCanTQid, (INT32 *)&oCanMsg);
>>      tm_wkafter(100);  // ~100ms
>>
>>      printf("WAKING");
>>      fflush(stdout);
>> }
>>
>> there is a task calling q_receive on the queue, but I have stubbed out
>> any work to keep it as simple as possible.
>>
>>
>> root@arm:~# cat /proc/xenomai/version
>> 2.6.3
>>
>> Here is xenomai/stat when running at ~40 %CPUfrom top. I presume that
>> ROOT/0 represents the
>> Xenomai/I-PIPE kernel. Nothing is reported as hogging the CPU....
>>
>> Every 2.0s: cat /proc/xenomai/stat                      Sat Jan  1
>> 00:09:03 2000
>>
>> CPU  PID    MSW        CSW        PF    STAT       %CPU  NAME
>>    0  0      0          186436     0     00500080   94.2  ROOT/0
>>    0  2882   16         427        0     00300380    0.0  MAIN
>>    0  2883   0          54128      0     00300184    1.0 onemsscheduler
>>    0  2884   0          542        0     00300184    0.0  FREE
>>    0  2885   0          1499       0     00300184    0.0  flsh
>>    0  2886   0          1          0     00300182    0.0  EWRN
>>    0  2887   0          45158      0     00300186    0.8  EEDT
>>    0  2888   0          53921      0     00300184    1.4  RESP
>>    0  2889   1          1          0     00300380    0.0  SERV
>>    0  2890   0          10784      0     00300184    0.4  CMND
>>    0  2891   2          1370       0     00300186    0.1  SERP
>>    0  2896   0          53080      0     00300184    0.8  SERO
>>    0  2899   0          536        0     00300186    0.0  CANP
>>    0  2900   0          1          0     00300182    0.0  CANG
>>    0  2901   0          1          0     00300182    0.0  CANE
>>    0  2902   0          315        0     00300182    0.0  CANT
>>    0  2903   1          1          0     00300380    0.0  CNMN
>>    0  2904   236        628        0     00300184    0.0  CIOW
>>    0  0      0          699350     0     00000000    1.0  IRQ83: [timer]
>>
>>
>> So questions are:
>>
>> - Why does the %CPU under xenomai/stat not reflect whats reported by top
>
> Because top reports the CPU consumed when Linux is active, which
> excludes Xenomai activity.
>
>> (where is the 40% going)?
>
> Good question.
>
>> - How can I track down the high CPU load?
>
> Could you obtain a report from Xenomai's rtps command? This one reports
> real-time cycles.
>
>> - Why would using printf and fflush make such a massive difference to
>> %CPU? The application is not busy waiting or doing any CPU intensive
>> work...
>
> Which kernel version, I-pipe release and CPU architecture are you
> running on?
>

Please ignore this question. I missed this info from your past mail, so 
ARM and 3.8 it seems.

-- 
Philippe.