Re: [Xenomai-core] rt timer jitter

2010-08-21 Thread Gilles Chanteperdrix
Krzysztof Błaszkowski wrote:
 Do you have any idea about reducing rt timer jitter ?
 I experience annoyingly big jitter in a thread which is supposed to run
 at 400us (i reckon this is nothing extra demanding from atom @1.6G)


 thread_task:2651 peak rt jitter -18470[ns], tsc delta 697450
 
 
 I must say it is 4 - 5 times worse if compared to rtai 3.7 / 2.6.27.19
 UP.
 
 I use now xenomai 2.5.4 with adeos 2.2-06 patch for same 2.6.27 kernel
 to make these comparisons more reliable.
 
 
 Can i do something with this ?

Ok. I had read that you had 400us jitter, this would have been pathological.

But 10us or 20us jitter on an ATOM is not.

The jitter on an idle system is not really significant, only the worst
case under several hours of heavy load is really significant.

-- 
Gilles.


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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Gilles Chanteperdrix
Krzysztof Błaszkowski wrote:
 Can i do something with this ?

Read TROUBLESHOOTING, FAQ, etc...

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Gilles.


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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Gilles Chanteperdrix
Krzysztof Błaszkowski wrote:
 Can i do something with this ?

Do you observe the same latencies with the latency test?


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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Krzysztof Błaszkowski
On Fri, 2010-08-20 at 18:01 +0200, Gilles Chanteperdrix wrote:
 Krzysztof Błaszkowski wrote:
  Can i do something with this ?
 
 Do you observe the same latencies with the latency test?
 

this test does not produce reliable results except some hints.

e.g. min. latency shifts about 1.5usec when i run on 2nd console dd
if=/dev/urandom of=/dev/null bs=16k.

as i recall max latency was more than 10 usec.



 


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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Krzysztof Błaszkowski
On Fri, 2010-08-20 at 18:06 +0200, Philippe Gerum wrote:
 On Fri, 2010-08-20 at 17:55 +0200, Krzysztof Błaszkowski wrote:
  Do you have any idea about reducing rt timer jitter ?
  I experience annoyingly big jitter in a thread which is supposed to run
  at 400us (i reckon this is nothing extra demanding from atom @1.6G)
  
  
  the thread's loop looks like:
  
  {
  function1()
  ..2()
  ..3()
  ..4()
  
  rt_task_wait_period()
  }
  
  (^yet another simplified model^)
 
 This is the typical pattern of the latency test. What figures do you get
 with:
 
 # /usr/xenomai/bin/latency -t0
 ...
 # /usr/xenomai/bin/latency -t1
 

t0:

RTS| -1.337| -0.039| 13.285|   0| 0|
00:02:13/00:02:13


i can't run t1 because of missing seno_timerbench.ko (i have no idea how
to find a config option which would build it)

-- 
Krzysztof Blaszkowski


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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Philippe Gerum
On Fri, 2010-08-20 at 18:20 +0200, Krzysztof Błaszkowski wrote:
 On Fri, 2010-08-20 at 18:06 +0200, Philippe Gerum wrote:
  On Fri, 2010-08-20 at 17:55 +0200, Krzysztof Błaszkowski wrote:
   Do you have any idea about reducing rt timer jitter ?
   I experience annoyingly big jitter in a thread which is supposed to run
   at 400us (i reckon this is nothing extra demanding from atom @1.6G)
   
   
   the thread's loop looks like:
   
   {
   function1()
   ..2()
   ..3()
   ..4()
   
   rt_task_wait_period()
   }
   
   (^yet another simplified model^)
  
  This is the typical pattern of the latency test. What figures do you get
  with:
  
  # /usr/xenomai/bin/latency -t0
  ...
  # /usr/xenomai/bin/latency -t1
  
 
 t0:
 
 RTS| -1.337| -0.039| 13.285|   0| 0|
 00:02:13/00:02:13
 

Those are common figures for user-space latency on the kind of hw you
run this test on.

 
 i can't run t1 because of missing seno_timerbench.ko (i have no idea how
 to find a config option which would build it)
 

Did you consider using the Search feature from
xconfig/gconfig/whatever, looking for timerbench?

config XENO_DRIVERS_TIMERBENCH
depends on XENO_SKIN_RTDM
tristate Timer benchmark driver
default y
help
Kernel-based benchmark driver for timer latency evaluation.
See testsuite/latency for a possible front-end.

If you run your app in kernel space, then -t1 is what you want to run.

-- 
Philippe.



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Re: [Xenomai-core] rt timer jitter

2010-08-20 Thread Philippe Gerum
On Fri, 2010-08-20 at 18:14 +0200, Krzysztof Błaszkowski wrote:
 On Fri, 2010-08-20 at 18:01 +0200, Gilles Chanteperdrix wrote:
  Krzysztof Błaszkowski wrote:
   Can i do something with this ?
  
  Do you observe the same latencies with the latency test?
  
 
 this test does not produce reliable results except some hints.
 
 e.g. min. latency shifts about 1.5usec when i run on 2nd console dd
 if=/dev/urandom of=/dev/null bs=16k.
 

and?

 as i recall max latency was more than 10 usec.
 

which is correct on your platform.

 
 
  
 
 

-- 
Philippe.



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